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A moderate set of locking updates:

Browse Source 
- A few extensions to the rwsem API and support for opportunistic
     spinning and lock stealing
 
   - lockdep selftest improvements
 
   - Documentation updates
 
   - Cleanups and small fixes all over the place
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Merge tag 'locking-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Thomas Gleixner:
 "A moderate set of locking updates:

   - A few extensions to the rwsem API and support for opportunistic
     spinning and lock stealing

   - lockdep selftest improvements

   - Documentation updates

   - Cleanups and small fixes all over the place"

* tag 'locking-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (21 commits)
  seqlock: kernel-doc: Specify when preemption is automatically altered
  seqlock: Prefix internal seqcount_t-only macros with a "do_"
  Documentation: seqlock: s/LOCKTYPE/LOCKNAME/g
  locking/rwsem: Remove reader optimistic spinning
  locking/rwsem: Enable reader optimistic lock stealing
  locking/rwsem: Prevent potential lock starvation
  locking/rwsem: Pass the current atomic count to rwsem_down_read_slowpath()
  locking/rwsem: Fold __down_{read,write}*()
  locking/rwsem: Introduce rwsem_write_trylock()
  locking/rwsem: Better collate rwsem_read_trylock()
  rwsem: Implement down_read_interruptible
  rwsem: Implement down_read_killable_nested
  refcount: Fix a kernel-doc markup
  completion: Drop init_completion define
  atomic: Update MAINTAINERS
  atomic: Delete obsolete documentation
  seqlock: Rename __seqprop() users
  lockdep/selftest: Add spin_nest_lock test
  lockdep/selftests: Fix PROVE_RAW_LOCK_NESTING
  seqlock: avoid -Wshadow warnings
  ...
This commit is contained in:
Linus Torvalds 2020-12-14 17:27:47 -08:00
commit e857b6fcc5
11 changed files with 254 additions and 1008 deletions
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664
Documentation/core-api/atomic_ops.rst
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@ -1,664 +0,0 @@
=======================================================
Semantics and Behavior of Atomic and Bitmask Operations
=======================================================
:Author: David S. Miller
This document is intended to serve as a guide to Linux port
maintainers on how to implement atomic counter, bitops, and spinlock
interfaces properly.
Atomic Type And Operations
==========================
The atomic_t type should be defined as a signed integer and
the atomic_long_t type as a signed long integer. Also, they should
be made opaque such that any kind of cast to a normal C integer type
will fail. Something like the following should suffice::
typedef struct { int counter; } atomic_t;
typedef struct { long counter; } atomic_long_t;
Historically, counter has been declared volatile. This is now discouraged.
See :ref:`Documentation/process/volatile-considered-harmful.rst
<volatile_considered_harmful>` for the complete rationale.
local_t is very similar to atomic_t. If the counter is per CPU and only
updated by one CPU, local_t is probably more appropriate. Please see
:ref:`Documentation/core-api/local_ops.rst <local_ops>` for the semantics of
local_t.
The first operations to implement for atomic_t's are the initializers and
plain writes. ::
#define ATOMIC_INIT(i) { (i) }
#define atomic_set(v, i) ((v)->counter = (i))
The first macro is used in definitions, such as::
static atomic_t my_counter = ATOMIC_INIT(1);
The initializer is atomic in that the return values of the atomic operations
are guaranteed to be correct reflecting the initialized value if the
initializer is used before runtime. If the initializer is used at runtime, a
proper implicit or explicit read memory barrier is needed before reading the
value with atomic_read from another thread.
As with all of the ``atomic_`` interfaces, replace the leading ``atomic_``
with ``atomic_long_`` to operate on atomic_long_t.
The second interface can be used at runtime, as in::
struct foo { atomic_t counter; };
...
struct foo *k;
k = kmalloc(sizeof(*k), GFP_KERNEL);
if (!k)
return -ENOMEM;
atomic_set(&k->counter, 0);
The setting is atomic in that the return values of the atomic operations by
all threads are guaranteed to be correct reflecting either the value that has
been set with this operation or set with another operation. A proper implicit
or explicit memory barrier is needed before the value set with the operation
is guaranteed to be readable with atomic_read from another thread.
Next, we have::
#define atomic_read(v) ((v)->counter)
which simply reads the counter value currently visible to the calling thread.
The read is atomic in that the return value is guaranteed to be one of the
values initialized or modified with the interface operations if a proper
implicit or explicit memory barrier is used after possible runtime
initialization by any other thread and the value is modified only with the
interface operations. atomic_read does not guarantee that the runtime
initialization by any other thread is visible yet, so the user of the
interface must take care of that with a proper implicit or explicit memory
barrier.
.. warning::
``atomic_read()`` and ``atomic_set()`` DO NOT IMPLY BARRIERS!
Some architectures may choose to use the volatile keyword, barriers, or
inline assembly to guarantee some degree of immediacy for atomic_read()
and atomic_set(). This is not uniformly guaranteed, and may change in
the future, so all users of atomic_t should treat atomic_read() and
atomic_set() as simple C statements that may be reordered or optimized
away entirely by the compiler or processor, and explicitly invoke the
appropriate compiler and/or memory barrier for each use case. Failure
to do so will result in code that may suddenly break when used with
different architectures or compiler optimizations, or even changes in
unrelated code which changes how the compiler optimizes the section
accessing atomic_t variables.
Properly aligned pointers, longs, ints, and chars (and unsigned
equivalents) may be atomically loaded from and stored to in the same
sense as described for atomic_read() and atomic_set(). The READ_ONCE()
and WRITE_ONCE() macros should be used to prevent the compiler from using
optimizations that might otherwise optimize accesses out of existence on
the one hand, or that might create unsolicited accesses on the other.
For example consider the following code::
while (a > 0)
do_something();
If the compiler can prove that do_something() does not store to the
variable a, then the compiler is within its rights transforming this to
the following::
if (a > 0)
for (;;)
do_something();
If you don't want the compiler to do this (and you probably don't), then
you should use something like the following::
while (READ_ONCE(a) > 0)
do_something();
Alternatively, you could place a barrier() call in the loop.
For another example, consider the following code::
tmp_a = a;
do_something_with(tmp_a);
do_something_else_with(tmp_a);
If the compiler can prove that do_something_with() does not store to the
variable a, then the compiler is within its rights to manufacture an
additional load as follows::
tmp_a = a;
do_something_with(tmp_a);
tmp_a = a;
do_something_else_with(tmp_a);
This could fatally confuse your code if it expected the same value
to be passed to do_something_with() and do_something_else_with().
The compiler would be likely to manufacture this additional load if
do_something_with() was an inline function that made very heavy use
of registers: reloading from variable a could save a flush to the
stack and later reload. To prevent the compiler from attacking your
code in this manner, write the following::
tmp_a = READ_ONCE(a);
do_something_with(tmp_a);
do_something_else_with(tmp_a);
For a final example, consider the following code, assuming that the
variable a is set at boot time before the second CPU is brought online
and never changed later, so that memory barriers are not needed::
if (a)
b = 9;
else
b = 42;
The compiler is within its rights to manufacture an additional store
by transforming the above code into the following::
b = 42;
if (a)
b = 9;
This could come as a fatal surprise to other code running concurrently
that expected b to never have the value 42 if a was zero. To prevent
the compiler from doing this, write something like::
if (a)
WRITE_ONCE(b, 9);
else
WRITE_ONCE(b, 42);
Don't even -think- about doing this without proper use of memory barriers,
locks, or atomic operations if variable a can change at runtime!
.. warning::
``READ_ONCE()`` OR ``WRITE_ONCE()`` DO NOT IMPLY A BARRIER!
Now, we move onto the atomic operation interfaces typically implemented with
the help of assembly code. ::
void atomic_add(int i, atomic_t *v);
void atomic_sub(int i, atomic_t *v);
void atomic_inc(atomic_t *v);
void atomic_dec(atomic_t *v);
These four routines add and subtract integral values to/from the given
atomic_t value. The first two routines pass explicit integers by
which to make the adjustment, whereas the latter two use an implicit
adjustment value of "1".
One very important aspect of these two routines is that they DO NOT
require any explicit memory barriers. They need only perform the
atomic_t counter update in an SMP safe manner.
Next, we have::
int atomic_inc_return(atomic_t *v);
int atomic_dec_return(atomic_t *v);
These routines add 1 and subtract 1, respectively, from the given
atomic_t and return the new counter value after the operation is
performed.
Unlike the above routines, it is required that these primitives
include explicit memory barriers that are performed before and after
the operation. It must be done such that all memory operations before
and after the atomic operation calls are strongly ordered with respect
to the atomic operation itself.
For example, it should behave as if a smp_mb() call existed both
before and after the atomic operation.
If the atomic instructions used in an implementation provide explicit
memory barrier semantics which satisfy the above requirements, that is
fine as well.
Let's move on::
int atomic_add_return(int i, atomic_t *v);
int atomic_sub_return(int i, atomic_t *v);
These behave just like atomic_{inc,dec}_return() except that an
explicit counter adjustment is given instead of the implicit "1".
This means that like atomic_{inc,dec}_return(), the memory barrier
semantics are required.
Next::
int atomic_inc_and_test(atomic_t *v);
int atomic_dec_and_test(atomic_t *v);
These two routines increment and decrement by 1, respectively, the
given atomic counter. They return a boolean indicating whether the
resulting counter value was zero or not.
Again, these primitives provide explicit memory barrier semantics around
the atomic operation::
int atomic_sub_and_test(int i, atomic_t *v);
This is identical to atomic_dec_and_test() except that an explicit
decrement is given instead of the implicit "1". This primitive must
provide explicit memory barrier semantics around the operation::
int atomic_add_negative(int i, atomic_t *v);
The given increment is added to the given atomic counter value. A boolean
is return which indicates whether the resulting counter value is negative.
This primitive must provide explicit memory barrier semantics around
the operation.
Then::
int atomic_xchg(atomic_t *v, int new);
This performs an atomic exchange operation on the atomic variable v, setting
the given new value. It returns the old value that the atomic variable v had
just before the operation.
atomic_xchg must provide explicit memory barriers around the operation. ::
int atomic_cmpxchg(atomic_t *v, int old, int new);
This performs an atomic compare exchange operation on the atomic value v,
with the given old and new values. Like all atomic_xxx operations,
atomic_cmpxchg will only satisfy its atomicity semantics as long as all
other accesses of \*v are performed through atomic_xxx operations.
atomic_cmpxchg must provide explicit memory barriers around the operation,
although if the comparison fails then no memory ordering guarantees are
required.
The semantics for atomic_cmpxchg are the same as those defined for 'cas'
below.
Finally::
int atomic_add_unless(atomic_t *v, int a, int u);
If the atomic value v is not equal to u, this function adds a to v, and
returns non zero. If v is equal to u then it returns zero. This is done as
an atomic operation.
atomic_add_unless must provide explicit memory barriers around the
operation unless it fails (returns 0).
atomic_inc_not_zero, equivalent to atomic_add_unless(v, 1, 0)
If a caller requires memory barrier semantics around an atomic_t
operation which does not return a value, a set of interfaces are
defined which accomplish this::
void smp_mb__before_atomic(void);
void smp_mb__after_atomic(void);
Preceding a non-value-returning read-modify-write atomic operation with
smp_mb__before_atomic() and following it with smp_mb__after_atomic()
provides the same full ordering that is provided by value-returning
read-modify-write atomic operations.
For example, smp_mb__before_atomic() can be used like so::
obj->dead = 1;
smp_mb__before_atomic();
atomic_dec(&obj->ref_count);
It makes sure that all memory operations preceding the atomic_dec()
call are strongly ordered with respect to the atomic counter
operation. In the above example, it guarantees that the assignment of
"1" to obj->dead will be globally visible to other cpus before the
atomic counter decrement.
Without the explicit smp_mb__before_atomic() call, the
implementation could legally allow the atomic counter update visible
to other cpus before the "obj->dead = 1;" assignment.
A missing memory barrier in the cases where they are required by the
atomic_t implementation above can have disastrous results. Here is
an example, which follows a pattern occurring frequently in the Linux
kernel. It is the use of atomic counters to implement reference
counting, and it works such that once the counter falls to zero it can
be guaranteed that no other entity can be accessing the object::
static void obj_list_add(struct obj *obj, struct list_head *head)
{
obj->active = 1;
list_add(&obj->list, head);
}
static void obj_list_del(struct obj *obj)
{
list_del(&obj->list);
obj->active = 0;
}
static void obj_destroy(struct obj *obj)
{
BUG_ON(obj->active);
kfree(obj);
}
struct obj *obj_list_peek(struct list_head *head)
{
if (!list_empty(head)) {
struct obj *obj;
obj = list_entry(head->next, struct obj, list);
atomic_inc(&obj->refcnt);
return obj;
}
return NULL;
}
void obj_poke(void)
{
struct obj *obj;
spin_lock(&global_list_lock);
obj = obj_list_peek(&global_list);
spin_unlock(&global_list_lock);
if (obj) {
obj->ops->poke(obj);
if (atomic_dec_and_test(&obj->refcnt))
obj_destroy(obj);
}
}
void obj_timeout(struct obj *obj)
{
spin_lock(&global_list_lock);
obj_list_del(obj);
spin_unlock(&global_list_lock);
if (atomic_dec_and_test(&obj->refcnt))
obj_destroy(obj);
}
.. note::
This is a simplification of the ARP queue management in the generic
neighbour discover code of the networking. Olaf Kirch found a bug wrt.
memory barriers in kfree_skb() that exposed the atomic_t memory barrier
requirements quite clearly.
Given the above scheme, it must be the case that the obj->active
update done by the obj list deletion be visible to other processors
before the atomic counter decrement is performed.
Otherwise, the counter could fall to zero, yet obj->active would still
be set, thus triggering the assertion in obj_destroy(). The error
sequence looks like this::
cpu 0 cpu 1
obj_poke() obj_timeout()
obj = obj_list_peek();
... gains ref to obj, refcnt=2
obj_list_del(obj);
obj->active = 0 ...
... visibility delayed ...
atomic_dec_and_test()
... refcnt drops to 1 ...
atomic_dec_and_test()
... refcount drops to 0 ...
obj_destroy()
BUG() triggers since obj->active
still seen as one
obj->active update visibility occurs
With the memory barrier semantics required of the atomic_t operations
which return values, the above sequence of memory visibility can never
happen. Specifically, in the above case the atomic_dec_and_test()
counter decrement would not become globally visible until the
obj->active update does.
As a historical note, 32-bit Sparc used to only allow usage of
24-bits of its atomic_t type. This was because it used 8 bits
as a spinlock for SMP safety. Sparc32 lacked a "compare and swap"
type instruction. However, 32-bit Sparc has since been moved over
to a "hash table of spinlocks" scheme, that allows the full 32-bit
counter to be realized. Essentially, an array of spinlocks are
indexed into based upon the address of the atomic_t being operated
on, and that lock protects the atomic operation. Parisc uses the
same scheme.
Another note is that the atomic_t operations returning values are
extremely slow on an old 386.
Atomic Bitmask
==============
We will now cover the atomic bitmask operations. You will find that
their SMP and memory barrier semantics are similar in shape and scope
to the atomic_t ops above.
Native atomic bit operations are defined to operate on objects aligned
to the size of an "unsigned long" C data type, and are least of that
size. The endianness of the bits within each "unsigned long" are the
native endianness of the cpu. ::
void set_bit(unsigned long nr, volatile unsigned long *addr);
void clear_bit(unsigned long nr, volatile unsigned long *addr);
void change_bit(unsigned long nr, volatile unsigned long *addr);
These routines set, clear, and change, respectively, the bit number
indicated by "nr" on the bit mask pointed to by "ADDR".
They must execute atomically, yet there are no implicit memory barrier
semantics required of these interfaces. ::
int test_and_set_bit(unsigned long nr, volatile unsigned long *addr);
int test_and_clear_bit(unsigned long nr, volatile unsigned long *addr);
int test_and_change_bit(unsigned long nr, volatile unsigned long *addr);
Like the above, except that these routines return a boolean which
indicates whether the changed bit was set _BEFORE_ the atomic bit
operation.
.. warning::
It is incredibly important that the value be a boolean, ie. "0" or "1".
Do not try to be fancy and save a few instructions by declaring the
above to return "long" and just returning something like "old_val &
mask" because that will not work.
For one thing, this return value gets truncated to int in many code
paths using these interfaces, so on 64-bit if the bit is set in the
upper 32-bits then testers will never see that.
One great example of where this problem crops up are the thread_info
flag operations. Routines such as test_and_set_ti_thread_flag() chop
the return value into an int. There are other places where things
like this occur as well.
These routines, like the atomic_t counter operations returning values,
must provide explicit memory barrier semantics around their execution.
All memory operations before the atomic bit operation call must be
made visible globally before the atomic bit operation is made visible.
Likewise, the atomic bit operation must be visible globally before any
subsequent memory operation is made visible. For example::
obj->dead = 1;
if (test_and_set_bit(0, &obj->flags))
/* ... */;
obj->killed = 1;
The implementation of test_and_set_bit() must guarantee that
"obj->dead = 1;" is visible to cpus before the atomic memory operation
done by test_and_set_bit() becomes visible. Likewise, the atomic
memory operation done by test_and_set_bit() must become visible before
"obj->killed = 1;" is visible.
Finally there is the basic operation::
int test_bit(unsigned long nr, __const__ volatile unsigned long *addr);
Which returns a boolean indicating if bit "nr" is set in the bitmask
pointed to by "addr".
If explicit memory barriers are required around {set,clear}_bit() (which do
not return a value, and thus does not need to provide memory barrier
semantics), two interfaces are provided::
void smp_mb__before_atomic(void);
void smp_mb__after_atomic(void);
They are used as follows, and are akin to their atomic_t operation
brothers::
/* All memory operations before this call will
* be globally visible before the clear_bit().
*/
smp_mb__before_atomic();
clear_bit( ... );
/* The clear_bit() will be visible before all
* subsequent memory operations.
*/
smp_mb__after_atomic();
There are two special bitops with lock barrier semantics (acquire/release,
same as spinlocks). These operate in the same way as their non-_lock/unlock
postfixed variants, except that they are to provide acquire/release semantics,
respectively. This means they can be used for bit_spin_trylock and
bit_spin_unlock type operations without specifying any more barriers. ::
int test_and_set_bit_lock(unsigned long nr, unsigned long *addr);
void clear_bit_unlock(unsigned long nr, unsigned long *addr);
void __clear_bit_unlock(unsigned long nr, unsigned long *addr);
The __clear_bit_unlock version is non-atomic, however it still implements
unlock barrier semantics. This can be useful if the lock itself is protecting
the other bits in the word.
Finally, there are non-atomic versions of the bitmask operations
provided. They are used in contexts where some other higher-level SMP
locking scheme is being used to protect the bitmask, and thus less
expensive non-atomic operations may be used in the implementation.
They have names similar to the above bitmask operation interfaces,
except that two underscores are prefixed to the interface name. ::
void __set_bit(unsigned long nr, volatile unsigned long *addr);
void __clear_bit(unsigned long nr, volatile unsigned long *addr);
void __change_bit(unsigned long nr, volatile unsigned long *addr);
int __test_and_set_bit(unsigned long nr, volatile unsigned long *addr);
int __test_and_clear_bit(unsigned long nr, volatile unsigned long *addr);
int __test_and_change_bit(unsigned long nr, volatile unsigned long *addr);
These non-atomic variants also do not require any special memory
barrier semantics.
The routines xchg() and cmpxchg() must provide the same exact
memory-barrier semantics as the atomic and bit operations returning
values.
.. note::
If someone wants to use xchg(), cmpxchg() and their variants,
linux/atomic.h should be included rather than asm/cmpxchg.h, unless the
code is in arch/* and can take care of itself.
Spinlocks and rwlocks have memory barrier expectations as well.
The rule to follow is simple:
1) When acquiring a lock, the implementation must make it globally
visible before any subsequent memory operation.
2) When releasing a lock, the implementation must make it such that
all previous memory operations are globally visible before the
lock release.
Which finally brings us to _atomic_dec_and_lock(). There is an
architecture-neutral version implemented in lib/dec_and_lock.c,
but most platforms will wish to optimize this in assembler. ::
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock);
Atomically decrement the given counter, and if will drop to zero
atomically acquire the given spinlock and perform the decrement
of the counter to zero. If it does not drop to zero, do nothing
with the spinlock.
It is actually pretty simple to get the memory barrier correct.
Simply satisfy the spinlock grab requirements, which is make
sure the spinlock operation is globally visible before any
subsequent memory operation.
We can demonstrate this operation more clearly if we define
an abstract atomic operation::
long cas(long *mem, long old, long new);
"cas" stands for "compare and swap". It atomically:
1) Compares "old" with the value currently at "mem".
2) If they are equal, "new" is written to "mem".
3) Regardless, the current value at "mem" is returned.
As an example usage, here is what an atomic counter update
might look like::
void example_atomic_inc(long *counter)
{
long old, new, ret;
while (1) {
old = *counter;
new = old + 1;
ret = cas(counter, old, new);
if (ret == old)
break;
}
}
Let's use cas() in order to build a pseudo-C atomic_dec_and_lock()::
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
{
long old, new, ret;
int went_to_zero;
went_to_zero = 0;
while (1) {
old = atomic_read(atomic);
new = old - 1;
if (new == 0) {
went_to_zero = 1;
spin_lock(lock);
}
ret = cas(atomic, old, new);
if (ret == old)
break;
if (went_to_zero) {
spin_unlock(lock);
went_to_zero = 0;
}
}
return went_to_zero;
}
Now, as far as memory barriers go, as long as spin_lock()
strictly orders all subsequent memory operations (including
the cas()) with respect to itself, things will be fine.
Said another way, _atomic_dec_and_lock() must guarantee that
a counter dropping to zero is never made visible before the
spinlock being acquired.
.. note::
Note that this also means that for the case where the counter is not
dropping to zero, there are no memory ordering requirements.

21
Documentation/locking/seqlock.rst
View File

@ -89,7 +89,7 @@ Read path::
.. _seqcount_locktype_t:
Sequence counters with associated locks (``seqcount_LOCKTYPE_t``)
Sequence counters with associated locks (``seqcount_LOCKNAME_t``)
-----------------------------------------------------------------
As discussed at :ref:`seqcount_t`, sequence count write side critical
@ -115,27 +115,26 @@ The following sequence counters with associated locks are defined:
- ``seqcount_mutex_t``
- ``seqcount_ww_mutex_t``
The plain seqcount read and write APIs branch out to the specific
seqcount_LOCKTYPE_t implementation at compile-time. This avoids kernel
API explosion per each new seqcount LOCKTYPE.
The sequence counter read and write APIs can take either a plain
seqcount_t or any of the seqcount_LOCKNAME_t variants above.
Initialization (replace "LOCKTYPE" with one of the supported locks)::
Initialization (replace "LOCKNAME" with one of the supported locks)::
/* dynamic */
seqcount_LOCKTYPE_t foo_seqcount;
seqcount_LOCKTYPE_init(&foo_seqcount, &lock);
seqcount_LOCKNAME_t foo_seqcount;
seqcount_LOCKNAME_init(&foo_seqcount, &lock);
/* static */
static seqcount_LOCKTYPE_t foo_seqcount =
SEQCNT_LOCKTYPE_ZERO(foo_seqcount, &lock);
static seqcount_LOCKNAME_t foo_seqcount =
SEQCNT_LOCKNAME_ZERO(foo_seqcount, &lock);
/* C99 struct init */
struct {
.seq = SEQCNT_LOCKTYPE_ZERO(foo.seq, &lock),
.seq = SEQCNT_LOCKNAME_ZERO(foo.seq, &lock),
} foo;
Write path: same as in :ref:`seqcount_t`, while running from a context
with the associated LOCKTYPE lock acquired.
with the associated write serialization lock acquired.
Read path: same as in :ref:`seqcount_t`.

2
MAINTAINERS
View File

@ -2982,6 +2982,8 @@ L: linux-kernel@vger.kernel.org
S: Maintained
F: arch/*/include/asm/atomic*.h
F: include/*/atomic*.h
F: include/linux/refcount.h
F: Documentation/atomic_*.txt
F: scripts/atomic/
ATTO EXPRESSSAS SAS/SATA RAID SCSI DRIVER

5
include/linux/completion.h
View File

@ -28,8 +28,7 @@ struct completion {
struct swait_queue_head wait;
};
#define init_completion_map(x, m) __init_completion(x)
#define init_completion(x) __init_completion(x)
#define init_completion_map(x, m) init_completion(x)
static inline void complete_acquire(struct completion *x) {}
static inline void complete_release(struct completion *x) {}
@ -82,7 +81,7 @@ static inline void complete_release(struct completion *x) {}
* This inline function will initialize a dynamically created completion
* structure.
*/
static inline void __init_completion(struct completion *x)
static inline void init_completion(struct completion *x)
{
x->done = 0;
init_swait_queue_head(&x->wait);

2
include/linux/refcount.h
View File

@ -101,7 +101,7 @@
struct mutex;
/**
* struct refcount_t - variant of atomic_t specialized for reference counts
* typedef refcount_t - variant of atomic_t specialized for reference counts
* @refs: atomic_t counter field
*
* The counter saturates at REFCOUNT_SATURATED and will not move once

3
include/linux/rwsem.h
View File

@ -123,6 +123,7 @@ static inline int rwsem_is_contended(struct rw_semaphore *sem)
* lock for reading
*/
extern void down_read(struct rw_semaphore *sem);
extern int __must_check down_read_interruptible(struct rw_semaphore *sem);
extern int __must_check down_read_killable(struct rw_semaphore *sem);
/*
@ -171,6 +172,7 @@ extern void downgrade_write(struct rw_semaphore *sem);
* See Documentation/locking/lockdep-design.rst for more details.)
*/
extern void down_read_nested(struct rw_semaphore *sem, int subclass);
extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass);
extern void down_write_nested(struct rw_semaphore *sem, int subclass);
extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
@ -191,6 +193,7 @@ extern void down_read_non_owner(struct rw_semaphore *sem);
extern void up_read_non_owner(struct rw_semaphore *sem);
#else
# define down_read_nested(sem, subclass) down_read(sem)
# define down_read_killable_nested(sem, subclass) down_read_killable(sem)
# define down_write_nest_lock(sem, nest_lock) down_write(sem)
# define down_write_nested(sem, subclass) down_write(sem)
# define down_write_killable_nested(sem, subclass) down_write_killable(sem)

121
include/linux/seqlock.h
View File

@ -307,10 +307,10 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
__seqprop_case((s), mutex, prop), \
__seqprop_case((s), ww_mutex, prop))
#define __seqcount_ptr(s) __seqprop(s, ptr)
#define __seqcount_sequence(s) __seqprop(s, sequence)
#define __seqcount_lock_preemptible(s) __seqprop(s, preemptible)
#define __seqcount_assert_lock_held(s) __seqprop(s, assert)
#define seqprop_ptr(s) __seqprop(s, ptr)
#define seqprop_sequence(s) __seqprop(s, sequence)
#define seqprop_preemptible(s) __seqprop(s, preemptible)
#define seqprop_assert(s) __seqprop(s, assert)
/**
* __read_seqcount_begin() - begin a seqcount_t read section w/o barrier
@ -328,13 +328,13 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
*/
#define __read_seqcount_begin(s) \
({ \
unsigned seq; \
unsigned __seq; \
\
while ((seq = __seqcount_sequence(s)) & 1) \
while ((__seq = seqprop_sequence(s)) & 1) \
cpu_relax(); \
\
kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \
seq; \
__seq; \
})
/**
@ -345,10 +345,10 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
*/
#define raw_read_seqcount_begin(s) \
({ \
unsigned seq = __read_seqcount_begin(s); \
unsigned _seq = __read_seqcount_begin(s); \
\
smp_rmb(); \
seq; \
_seq; \
})
/**
@ -359,7 +359,7 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
*/
#define read_seqcount_begin(s) \
({ \
seqcount_lockdep_reader_access(__seqcount_ptr(s)); \
seqcount_lockdep_reader_access(seqprop_ptr(s)); \
raw_read_seqcount_begin(s); \
})
@ -376,11 +376,11 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
*/
#define raw_read_seqcount(s) \
({ \
unsigned seq = __seqcount_sequence(s); \
unsigned __seq = seqprop_sequence(s); \
\
smp_rmb(); \
kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \
seq; \
__seq; \
})
/**
@ -425,9 +425,9 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
* Return: true if a read section retry is required, else false
*/
#define __read_seqcount_retry(s, start) \
__read_seqcount_t_retry(__seqcount_ptr(s), start)
do___read_seqcount_retry(seqprop_ptr(s), start)
static inline int __read_seqcount_t_retry(const seqcount_t *s, unsigned start)
static inline int do___read_seqcount_retry(const seqcount_t *s, unsigned start)
{
kcsan_atomic_next(0);
return unlikely(READ_ONCE(s->sequence) != start);
@ -445,27 +445,29 @@ static inline int __read_seqcount_t_retry(const seqcount_t *s, unsigned start)
* Return: true if a read section retry is required, else false
*/
#define read_seqcount_retry(s, start) \
read_seqcount_t_retry(__seqcount_ptr(s), start)
do_read_seqcount_retry(seqprop_ptr(s), start)
static inline int read_seqcount_t_retry(const seqcount_t *s, unsigned start)
static inline int do_read_seqcount_retry(const seqcount_t *s, unsigned start)
{
smp_rmb();
return __read_seqcount_t_retry(s, start);
return do___read_seqcount_retry(s, start);
}
/**
* raw_write_seqcount_begin() - start a seqcount_t write section w/o lockdep
* @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
*
* Context: check write_seqcount_begin()
*/
#define raw_write_seqcount_begin(s) \
do { \
if (__seqcount_lock_preemptible(s)) \
if (seqprop_preemptible(s)) \
preempt_disable(); \
\
raw_write_seqcount_t_begin(__seqcount_ptr(s)); \
do_raw_write_seqcount_begin(seqprop_ptr(s)); \
} while (0)
static inline void raw_write_seqcount_t_begin(seqcount_t *s)
static inline void do_raw_write_seqcount_begin(seqcount_t *s)
{
kcsan_nestable_atomic_begin();
s->sequence++;
@ -475,16 +477,18 @@ static inline void raw_write_seqcount_t_begin(seqcount_t *s)
/**
* raw_write_seqcount_end() - end a seqcount_t write section w/o lockdep
* @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
*
* Context: check write_seqcount_end()
*/
#define raw_write_seqcount_end(s) \
do { \
raw_write_seqcount_t_end(__seqcount_ptr(s)); \
do_raw_write_seqcount_end(seqprop_ptr(s)); \
\
if (__seqcount_lock_preemptible(s)) \
if (seqprop_preemptible(s)) \
preempt_enable(); \
} while (0)
static inline void raw_write_seqcount_t_end(seqcount_t *s)
static inline void do_raw_write_seqcount_end(seqcount_t *s)
{
smp_wmb();
s->sequence++;
@ -498,20 +502,21 @@ static inline void raw_write_seqcount_t_end(seqcount_t *s)
* @subclass: lockdep nesting level
*
* See Documentation/locking/lockdep-design.rst
* Context: check write_seqcount_begin()
*/
#define write_seqcount_begin_nested(s, subclass) \
do { \
__seqcount_assert_lock_held(s); \
seqprop_assert(s); \
\
if (__seqcount_lock_preemptible(s)) \
if (seqprop_preemptible(s)) \
preempt_disable(); \
\
write_seqcount_t_begin_nested(__seqcount_ptr(s), subclass); \
do_write_seqcount_begin_nested(seqprop_ptr(s), subclass); \
} while (0)
static inline void write_seqcount_t_begin_nested(seqcount_t *s, int subclass)
static inline void do_write_seqcount_begin_nested(seqcount_t *s, int subclass)
{
raw_write_seqcount_t_begin(s);
do_raw_write_seqcount_begin(s);
seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_);
}
@ -519,46 +524,46 @@ static inline void write_seqcount_t_begin_nested(seqcount_t *s, int subclass)
* write_seqcount_begin() - start a seqcount_t write side critical section
* @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
*
* write_seqcount_begin opens a write side critical section of the given
* seqcount_t.
*
* Context: seqcount_t write side critical sections must be serialized and
* non-preemptible. If readers can be invoked from hardirq or softirq
* Context: sequence counter write side sections must be serialized and
* non-preemptible. Preemption will be automatically disabled if and
* only if the seqcount write serialization lock is associated, and
* preemptible. If readers can be invoked from hardirq or softirq
* context, interrupts or bottom halves must be respectively disabled.
*/
#define write_seqcount_begin(s) \
do { \
__seqcount_assert_lock_held(s); \
seqprop_assert(s); \
\
if (__seqcount_lock_preemptible(s)) \
if (seqprop_preemptible(s)) \
preempt_disable(); \
\
write_seqcount_t_begin(__seqcount_ptr(s)); \
do_write_seqcount_begin(seqprop_ptr(s)); \
} while (0)
static inline void write_seqcount_t_begin(seqcount_t *s)
static inline void do_write_seqcount_begin(seqcount_t *s)
{
write_seqcount_t_begin_nested(s, 0);
do_write_seqcount_begin_nested(s, 0);
}
/**
* write_seqcount_end() - end a seqcount_t write side critical section
* @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
*
* The write section must've been opened with write_seqcount_begin().
* Context: Preemption will be automatically re-enabled if and only if
* the seqcount write serialization lock is associated, and preemptible.
*/
#define write_seqcount_end(s) \
do { \
write_seqcount_t_end(__seqcount_ptr(s)); \
do_write_seqcount_end(seqprop_ptr(s)); \
\
if (__seqcount_lock_preemptible(s)) \
if (seqprop_preemptible(s)) \
preempt_enable(); \
} while (0)
static inline void write_seqcount_t_end(seqcount_t *s)
static inline void do_write_seqcount_end(seqcount_t *s)
{
seqcount_release(&s->dep_map, _RET_IP_);
raw_write_seqcount_t_end(s);
do_raw_write_seqcount_end(s);
}
/**
@ -603,9 +608,9 @@ static inline void write_seqcount_t_end(seqcount_t *s)
* }
*/
#define raw_write_seqcount_barrier(s) \
raw_write_seqcount_t_barrier(__seqcount_ptr(s))
do_raw_write_seqcount_barrier(seqprop_ptr(s))
static inline void raw_write_seqcount_t_barrier(seqcount_t *s)
static inline void do_raw_write_seqcount_barrier(seqcount_t *s)
{
kcsan_nestable_atomic_begin();
s->sequence++;
@ -623,9 +628,9 @@ static inline void raw_write_seqcount_t_barrier(seqcount_t *s)
* will complete successfully and see data older than this.
*/
#define write_seqcount_invalidate(s) \
write_seqcount_t_invalidate(__seqcount_ptr(s))
do_write_seqcount_invalidate(seqprop_ptr(s))
static inline void write_seqcount_t_invalidate(seqcount_t *s)
static inline void do_write_seqcount_invalidate(seqcount_t *s)
{
smp_wmb();
kcsan_nestable_atomic_begin();
@ -865,9 +870,9 @@ static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
}
/*
* For all seqlock_t write side functions, use write_seqcount_*t*_begin()
* instead of the generic write_seqcount_begin(). This way, no redundant
* lockdep_assert_held() checks are added.
* For all seqlock_t write side functions, use the the internal
* do_write_seqcount_begin() instead of generic write_seqcount_begin().
* This way, no redundant lockdep_assert_held() checks are added.
*/
/**
@ -886,7 +891,7 @@ static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
static inline void write_seqlock(seqlock_t *sl)
{
spin_lock(&sl->lock);
write_seqcount_t_begin(&sl->seqcount.seqcount);
do_write_seqcount_begin(&sl->seqcount.seqcount);
}
/**
@ -898,7 +903,7 @@ static inline void write_seqlock(seqlock_t *sl)
*/
static inline void write_sequnlock(seqlock_t *sl)
{
write_seqcount_t_end(&sl->seqcount.seqcount);
do_write_seqcount_end(&sl->seqcount.seqcount);
spin_unlock(&sl->lock);
}
@ -912,7 +917,7 @@ static inline void write_sequnlock(seqlock_t *sl)
static inline void write_seqlock_bh(seqlock_t *sl)
{
spin_lock_bh(&sl->lock);
write_seqcount_t_begin(&sl->seqcount.seqcount);
do_write_seqcount_begin(&sl->seqcount.seqcount);
}
/**
@ -925,7 +930,7 @@ static inline void write_seqlock_bh(seqlock_t *sl)
*/
static inline void write_sequnlock_bh(seqlock_t *sl)
{
write_seqcount_t_end(&sl->seqcount.seqcount);
do_write_seqcount_end(&sl->seqcount.seqcount);
spin_unlock_bh(&sl->lock);
}
@ -939,7 +944,7 @@ static inline void write_sequnlock_bh(seqlock_t *sl)
static inline void write_seqlock_irq(seqlock_t *sl)
{
spin_lock_irq(&sl->lock);
write_seqcount_t_begin(&sl->seqcount.seqcount);
do_write_seqcount_begin(&sl->seqcount.seqcount);
}
/**
@ -951,7 +956,7 @@ static inline void write_seqlock_irq(seqlock_t *sl)
*/
static inline void write_sequnlock_irq(seqlock_t *sl)
{
write_seqcount_t_end(&sl->seqcount.seqcount);
do_write_seqcount_end(&sl->seqcount.seqcount);
spin_unlock_irq(&sl->lock);
}
@ -960,7 +965,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
unsigned long flags;
spin_lock_irqsave(&sl->lock, flags);
write_seqcount_t_begin(&sl->seqcount.seqcount);
do_write_seqcount_begin(&sl->seqcount.seqcount);
return flags;
}
@ -989,7 +994,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
static inline void
write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags)
{
write_seqcount_t_end(&sl->seqcount.seqcount);
do_write_seqcount_end(&sl->seqcount.seqcount);
spin_unlock_irqrestore(&sl->lock, flags);
}

2
kernel/futex.c
View File

@ -310,8 +310,6 @@ static inline bool should_fail_futex(bool fshared)
#ifdef CONFIG_COMPAT
static void compat_exit_robust_list(struct task_struct *curr);
#else
static inline void compat_exit_robust_list(struct task_struct *curr) { }
#endif
/*

6
kernel/locking/lock_events_list.h
View File

@ -56,13 +56,11 @@ LOCK_EVENT(rwsem_sleep_reader) /* # of reader sleeps */
LOCK_EVENT(rwsem_sleep_writer) /* # of writer sleeps */
LOCK_EVENT(rwsem_wake_reader) /* # of reader wakeups */
LOCK_EVENT(rwsem_wake_writer) /* # of writer wakeups */
LOCK_EVENT(rwsem_opt_rlock) /* # of opt-acquired read locks */
LOCK_EVENT(rwsem_opt_wlock) /* # of opt-acquired write locks */
LOCK_EVENT(rwsem_opt_lock) /* # of opt-acquired write locks */
LOCK_EVENT(rwsem_opt_fail) /* # of failed optspins */
LOCK_EVENT(rwsem_opt_nospin) /* # of disabled optspins */
LOCK_EVENT(rwsem_opt_norspin) /* # of disabled reader-only optspins */
LOCK_EVENT(rwsem_opt_rlock2) /* # of opt-acquired 2ndary read locks */
LOCK_EVENT(rwsem_rlock) /* # of read locks acquired */
LOCK_EVENT(rwsem_rlock_steal) /* # of read locks by lock stealing */
LOCK_EVENT(rwsem_rlock_fast) /* # of fast read locks acquired */
LOCK_EVENT(rwsem_rlock_fail) /* # of failed read lock acquisitions */
LOCK_EVENT(rwsem_rlock_handoff) /* # of read lock handoffs */

385
kernel/locking/rwsem.c
View File

@ -31,19 +31,13 @@
#include "lock_events.h"
/*
* The least significant 3 bits of the owner value has the following
* The least significant 2 bits of the owner value has the following
* meanings when set.
* - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
* - Bit 1: RWSEM_RD_NONSPINNABLE - Readers cannot spin on this lock.
* - Bit 2: RWSEM_WR_NONSPINNABLE - Writers cannot spin on this lock.
* - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
*
* When the rwsem is either owned by an anonymous writer, or it is
* reader-owned, but a spinning writer has timed out, both nonspinnable
* bits will be set to disable optimistic spinning by readers and writers.
* In the later case, the last unlocking reader should then check the
* writer nonspinnable bit and clear it only to give writers preference
* to acquire the lock via optimistic spinning, but not readers. Similar
* action is also done in the reader slowpath.
* When the rwsem is reader-owned and a spinning writer has timed out,
* the nonspinnable bit will be set to disable optimistic spinning.
* When a writer acquires a rwsem, it puts its task_struct pointer
* into the owner field. It is cleared after an unlock.
@ -59,46 +53,14 @@
* is involved. Ideally we would like to track all the readers that own
* a rwsem, but the overhead is simply too big.
*
* Reader optimistic spinning is helpful when the reader critical section
* is short and there aren't that many readers around. It makes readers
* relatively more preferred than writers. When a writer times out spinning
* on a reader-owned lock and set the nospinnable bits, there are two main
* reasons for that.
*
* 1) The reader critical section is long, perhaps the task sleeps after
* acquiring the read lock.
* 2) There are just too many readers contending the lock causing it to
* take a while to service all of them.
*
* In the former case, long reader critical section will impede the progress
* of writers which is usually more important for system performance. In
* the later case, reader optimistic spinning tends to make the reader
* groups that contain readers that acquire the lock together smaller
* leading to more of them. That may hurt performance in some cases. In
* other words, the setting of nonspinnable bits indicates that reader
* optimistic spinning may not be helpful for those workloads that cause
* it.
*
* Therefore, any writers that had observed the setting of the writer
* nonspinnable bit for a given rwsem after they fail to acquire the lock
* via optimistic spinning will set the reader nonspinnable bit once they
* acquire the write lock. Similarly, readers that observe the setting
* of reader nonspinnable bit at slowpath entry will set the reader
* nonspinnable bits when they acquire the read lock via the wakeup path.
*
* Once the reader nonspinnable bit is on, it will only be reset when
* a writer is able to acquire the rwsem in the fast path or somehow a
* reader or writer in the slowpath doesn't observe the nonspinable bit.
*
* This is to discourage reader optmistic spinning on that particular
* rwsem and make writers more preferred. This adaptive disabling of reader
* optimistic spinning will alleviate the negative side effect of this
* feature.
* A fast path reader optimistic lock stealing is supported when the rwsem
* is previously owned by a writer and the following conditions are met:
* - OSQ is empty
* - rwsem is not currently writer owned
* - the handoff isn't set.
*/
#define RWSEM_READER_OWNED (1UL << 0)
#define RWSEM_RD_NONSPINNABLE (1UL << 1)
#define RWSEM_WR_NONSPINNABLE (1UL << 2)
#define RWSEM_NONSPINNABLE (RWSEM_RD_NONSPINNABLE | RWSEM_WR_NONSPINNABLE)
#define RWSEM_NONSPINNABLE (1UL << 1)
#define RWSEM_OWNER_FLAGS_MASK (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
#ifdef CONFIG_DEBUG_RWSEMS
@ -203,7 +165,7 @@ static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
struct task_struct *owner)
{
unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
(atomic_long_read(&sem->owner) & RWSEM_RD_NONSPINNABLE);
(atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE);
atomic_long_set(&sem->owner, val);
}
@ -270,12 +232,31 @@ static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
owner | RWSEM_NONSPINNABLE));
}
static inline bool rwsem_read_trylock(struct rw_semaphore *sem)
static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)
{
long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
if (WARN_ON_ONCE(cnt < 0))
*cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
if (WARN_ON_ONCE(*cntp < 0))
rwsem_set_nonspinnable(sem);
return !(cnt & RWSEM_READ_FAILED_MASK);
if (!(*cntp & RWSEM_READ_FAILED_MASK)) {
rwsem_set_reader_owned(sem);
return true;
}
return false;
}
static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
{
long tmp = RWSEM_UNLOCKED_VALUE;
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
rwsem_set_owner(sem);
return true;
}
return false;
}
/*
@ -353,7 +334,6 @@ struct rwsem_waiter {
struct task_struct *task;
enum rwsem_waiter_type type;
unsigned long timeout;
unsigned long last_rowner;
};
#define rwsem_first_waiter(sem) \
list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
@ -467,10 +447,6 @@ static void rwsem_mark_wake(struct rw_semaphore *sem,
* the reader is copied over.
*/
owner = waiter->task;
if (waiter->last_rowner & RWSEM_RD_NONSPINNABLE) {
owner = (void *)((unsigned long)owner | RWSEM_RD_NONSPINNABLE);
lockevent_inc(rwsem_opt_norspin);
}
__rwsem_set_reader_owned(sem, owner);
}
@ -601,30 +577,6 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
}
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
/*
* Try to acquire read lock before the reader is put on wait queue.
* Lock acquisition isn't allowed if the rwsem is locked or a writer handoff
* is ongoing.
*/
static inline bool rwsem_try_read_lock_unqueued(struct rw_semaphore *sem)
{
long count = atomic_long_read(&sem->count);
if (count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))
return false;
count = atomic_long_fetch_add_acquire(RWSEM_READER_BIAS, &sem->count);
if (!(count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
rwsem_set_reader_owned(sem);
lockevent_inc(rwsem_opt_rlock);
return true;
}
/* Back out the change */
atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
return false;
}
/*
* Try to acquire write lock before the writer has been put on wait queue.
*/
@ -636,7 +588,7 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
count | RWSEM_WRITER_LOCKED)) {
rwsem_set_owner(sem);
lockevent_inc(rwsem_opt_wlock);
lockevent_inc(rwsem_opt_lock);
return true;
}
}
@ -652,8 +604,7 @@ static inline bool owner_on_cpu(struct task_struct *owner)
return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
}
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
unsigned long nonspinnable)
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
{
struct task_struct *owner;
unsigned long flags;
@ -670,7 +621,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
/*
* Don't check the read-owner as the entry may be stale.
*/
if ((flags & nonspinnable) ||
if ((flags & RWSEM_NONSPINNABLE) ||
(owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
ret = false;
rcu_read_unlock();
@ -700,9 +651,9 @@ enum owner_state {
#define OWNER_SPINNABLE (OWNER_NULL | OWNER_WRITER | OWNER_READER)
static inline enum owner_state
rwsem_owner_state(struct task_struct *owner, unsigned long flags, unsigned long nonspinnable)
rwsem_owner_state(struct task_struct *owner, unsigned long flags)
{
if (flags & nonspinnable)
if (flags & RWSEM_NONSPINNABLE)
return OWNER_NONSPINNABLE;
if (flags & RWSEM_READER_OWNED)
@ -712,14 +663,14 @@ rwsem_owner_state(struct task_struct *owner, unsigned long flags, unsigned long
}
static noinline enum owner_state
rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
rwsem_spin_on_owner(struct rw_semaphore *sem)
{
struct task_struct *new, *owner;
unsigned long flags, new_flags;
enum owner_state state;
owner = rwsem_owner_flags(sem, &flags);
state = rwsem_owner_state(owner, flags, nonspinnable);
state = rwsem_owner_state(owner, flags);
if (state != OWNER_WRITER)
return state;
@ -733,7 +684,7 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
*/
new = rwsem_owner_flags(sem, &new_flags);
if ((new != owner) || (new_flags != flags)) {
state = rwsem_owner_state(new, new_flags, nonspinnable);
state = rwsem_owner_state(new, new_flags);
break;
}
@ -782,14 +733,12 @@ static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
return sched_clock() + delta;
}
static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
{
bool taken = false;
int prev_owner_state = OWNER_NULL;
int loop = 0;
u64 rspin_threshold = 0;
unsigned long nonspinnable = wlock ? RWSEM_WR_NONSPINNABLE
: RWSEM_RD_NONSPINNABLE;
preempt_disable();
@ -806,15 +755,14 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
for (;;) {
enum owner_state owner_state;
owner_state = rwsem_spin_on_owner(sem, nonspinnable);
owner_state = rwsem_spin_on_owner(sem);
if (!(owner_state & OWNER_SPINNABLE))
break;
/*
* Try to acquire the lock
*/
taken = wlock ? rwsem_try_write_lock_unqueued(sem)
: rwsem_try_read_lock_unqueued(sem);
taken = rwsem_try_write_lock_unqueued(sem);
if (taken)
break;
@ -822,7 +770,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
/*
* Time-based reader-owned rwsem optimistic spinning
*/
if (wlock && (owner_state == OWNER_READER)) {
if (owner_state == OWNER_READER) {
/*
* Re-initialize rspin_threshold every time when
* the owner state changes from non-reader to reader.
@ -831,7 +779,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
* the beginning of the 2nd reader phase.
*/
if (prev_owner_state != OWNER_READER) {
if (rwsem_test_oflags(sem, nonspinnable))
if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
break;
rspin_threshold = rwsem_rspin_threshold(sem);
loop = 0;
@ -907,78 +855,30 @@ done:
}
/*
* Clear the owner's RWSEM_WR_NONSPINNABLE bit if it is set. This should
* Clear the owner's RWSEM_NONSPINNABLE bit if it is set. This should
* only be called when the reader count reaches 0.
*
* This give writers better chance to acquire the rwsem first before
* readers when the rwsem was being held by readers for a relatively long
* period of time. Race can happen that an optimistic spinner may have
* just stolen the rwsem and set the owner, but just clearing the
* RWSEM_WR_NONSPINNABLE bit will do no harm anyway.
*/
static inline void clear_wr_nonspinnable(struct rw_semaphore *sem)
static inline void clear_nonspinnable(struct rw_semaphore *sem)
{
if (rwsem_test_oflags(sem, RWSEM_WR_NONSPINNABLE))
atomic_long_andnot(RWSEM_WR_NONSPINNABLE, &sem->owner);
if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
atomic_long_andnot(RWSEM_NONSPINNABLE, &sem->owner);
}
/*
* This function is called when the reader fails to acquire the lock via
* optimistic spinning. In this case we will still attempt to do a trylock
* when comparing the rwsem state right now with the state when entering
* the slowpath indicates that the reader is still in a valid reader phase.
* This happens when the following conditions are true:
*
* 1) The lock is currently reader owned, and
* 2) The lock is previously not reader-owned or the last read owner changes.
*
* In the former case, we have transitioned from a writer phase to a
* reader-phase while spinning. In the latter case, it means the reader
* phase hasn't ended when we entered the optimistic spinning loop. In
* both cases, the reader is eligible to acquire the lock. This is the
* secondary path where a read lock is acquired optimistically.
*
* The reader non-spinnable bit wasn't set at time of entry or it will
* not be here at all.
*/
static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
unsigned long last_rowner)
{
unsigned long owner = atomic_long_read(&sem->owner);
if (!(owner & RWSEM_READER_OWNED))
return false;
if (((owner ^ last_rowner) & ~RWSEM_OWNER_FLAGS_MASK) &&
rwsem_try_read_lock_unqueued(sem)) {
lockevent_inc(rwsem_opt_rlock2);
lockevent_add(rwsem_opt_fail, -1);
return true;
}
return false;
}
#else
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
unsigned long nonspinnable)
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
{
return false;
}
static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem)
{
return false;
}
static inline void clear_wr_nonspinnable(struct rw_semaphore *sem) { }
static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
unsigned long last_rowner)
{
return false;
}
static inline void clear_nonspinnable(struct rw_semaphore *sem) { }
static inline int
rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
rwsem_spin_on_owner(struct rw_semaphore *sem)
{
return 0;
}
@ -989,36 +889,35 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
* Wait for the read lock to be granted
*/
static struct rw_semaphore __sched *
rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, int state)
{
long count, adjustment = -RWSEM_READER_BIAS;
long adjustment = -RWSEM_READER_BIAS;
long rcnt = (count >> RWSEM_READER_SHIFT);
struct rwsem_waiter waiter;
DEFINE_WAKE_Q(wake_q);
bool wake = false;
/*
* Save the current read-owner of rwsem, if available, and the
* reader nonspinnable bit.
* To prevent a constant stream of readers from starving a sleeping
* waiter, don't attempt optimistic lock stealing if the lock is
* currently owned by readers.
*/
waiter.last_rowner = atomic_long_read(&sem->owner);
if (!(waiter.last_rowner & RWSEM_READER_OWNED))
waiter.last_rowner &= RWSEM_RD_NONSPINNABLE;
if (!rwsem_can_spin_on_owner(sem, RWSEM_RD_NONSPINNABLE))
if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
(rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))
goto queue;
/*
* Undo read bias from down_read() and do optimistic spinning.
* Reader optimistic lock stealing.
*/
atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
adjustment = 0;
if (rwsem_optimistic_spin(sem, false)) {
/* rwsem_optimistic_spin() implies ACQUIRE on success */
if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF))) {
rwsem_set_reader_owned(sem);
lockevent_inc(rwsem_rlock_steal);
/*
* Wake up other readers in the wait list if the front
* waiter is a reader.
* Wake up other readers in the wait queue if it is
* the first reader.
*/
if ((atomic_long_read(&sem->count) & RWSEM_FLAG_WAITERS)) {
if ((rcnt == 1) && (count & RWSEM_FLAG_WAITERS)) {
raw_spin_lock_irq(&sem->wait_lock);
if (!list_empty(&sem->wait_list))
rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
@ -1027,9 +926,6 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
wake_up_q(&wake_q);
}
return sem;
} else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) {
/* rwsem_reader_phase_trylock() implies ACQUIRE on success */
return sem;
}
queue:
@ -1045,7 +941,7 @@ queue:
* exit the slowpath and return immediately as its
* RWSEM_READER_BIAS has already been set in the count.
*/
if (adjustment && !(atomic_long_read(&sem->count) &
if (!(atomic_long_read(&sem->count) &
(RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
/* Provide lock ACQUIRE */
smp_acquire__after_ctrl_dep();
@ -1059,10 +955,7 @@ queue:
list_add_tail(&waiter.list, &sem->wait_list);
/* we're now waiting on the lock, but no longer actively locking */
if (adjustment)
count = atomic_long_add_return(adjustment, &sem->count);
else
count = atomic_long_read(&sem->count);
count = atomic_long_add_return(adjustment, &sem->count);
/*
* If there are no active locks, wake the front queued process(es).
@ -1071,7 +964,7 @@ queue:
* wake our own waiter to join the existing active readers !
*/
if (!(count & RWSEM_LOCK_MASK)) {
clear_wr_nonspinnable(sem);
clear_nonspinnable(sem);
wake = true;
}
if (wake || (!(count & RWSEM_WRITER_MASK) &&
@ -1116,19 +1009,6 @@ out_nolock:
return ERR_PTR(-EINTR);
}
/*
* This function is called by the a write lock owner. So the owner value
* won't get changed by others.
*/
static inline void rwsem_disable_reader_optspin(struct rw_semaphore *sem,
bool disable)
{
if (unlikely(disable)) {
atomic_long_or(RWSEM_RD_NONSPINNABLE, &sem->owner);
lockevent_inc(rwsem_opt_norspin);
}
}
/*
* Wait until we successfully acquire the write lock
*/
@ -1136,26 +1016,17 @@ static struct rw_semaphore *
rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
{
long count;
bool disable_rspin;
enum writer_wait_state wstate;
struct rwsem_waiter waiter;
struct rw_semaphore *ret = sem;
DEFINE_WAKE_Q(wake_q);
/* do optimistic spinning and steal lock if possible */
if (rwsem_can_spin_on_owner(sem, RWSEM_WR_NONSPINNABLE) &&
rwsem_optimistic_spin(sem, true)) {
if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) {
/* rwsem_optimistic_spin() implies ACQUIRE on success */
return sem;
}
/*
* Disable reader optimistic spinning for this rwsem after
* acquiring the write lock when the setting of the nonspinnable
* bits are observed.
*/
disable_rspin = atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE;
/*
* Optimistic spinning failed, proceed to the slowpath
* and block until we can acquire the sem.
@ -1224,7 +1095,7 @@ wait:
* without sleeping.
*/
if (wstate == WRITER_HANDOFF &&
rwsem_spin_on_owner(sem, RWSEM_NONSPINNABLE) == OWNER_NULL)
rwsem_spin_on_owner(sem) == OWNER_NULL)
goto trylock_again;
/* Block until there are no active lockers. */
@ -1266,7 +1137,6 @@ trylock_again:
}
__set_current_state(TASK_RUNNING);
list_del(&waiter.list);
rwsem_disable_reader_optspin(sem, disable_rspin);
raw_spin_unlock_irq(&sem->wait_lock);
lockevent_inc(rwsem_wlock);
@ -1335,26 +1205,31 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
/*
* lock for reading
*/
static inline int __down_read_common(struct rw_semaphore *sem, int state)
{
long count;
if (!rwsem_read_trylock(sem, &count)) {
if (IS_ERR(rwsem_down_read_slowpath(sem, count, state)))
return -EINTR;
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
}
return 0;
}
static inline void __down_read(struct rw_semaphore *sem)
{
if (!rwsem_read_trylock(sem)) {
rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE);
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
} else {
rwsem_set_reader_owned(sem);
}
__down_read_common(sem, TASK_UNINTERRUPTIBLE);
}
static inline int __down_read_interruptible(struct rw_semaphore *sem)
{
return __down_read_common(sem, TASK_INTERRUPTIBLE);
}
static inline int __down_read_killable(struct rw_semaphore *sem)
{
if (!rwsem_read_trylock(sem)) {
if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE)))
return -EINTR;
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
} else {
rwsem_set_reader_owned(sem);
}
return 0;
return __down_read_common(sem, TASK_KILLABLE);
}
static inline int __down_read_trylock(struct rw_semaphore *sem)
@ -1380,44 +1255,30 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
/*
* lock for writing
*/
static inline int __down_write_common(struct rw_semaphore *sem, int state)
{
if (unlikely(!rwsem_write_trylock(sem))) {
if (IS_ERR(rwsem_down_write_slowpath(sem, state)))
return -EINTR;
}
return 0;
}
static inline void __down_write(struct rw_semaphore *sem)
{
long tmp = RWSEM_UNLOCKED_VALUE;
if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
RWSEM_WRITER_LOCKED)))
rwsem_down_write_slowpath(sem, TASK_UNINTERRUPTIBLE);
else
rwsem_set_owner(sem);
__down_write_common(sem, TASK_UNINTERRUPTIBLE);
}
static inline int __down_write_killable(struct rw_semaphore *sem)
{
long tmp = RWSEM_UNLOCKED_VALUE;
if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
RWSEM_WRITER_LOCKED))) {
if (IS_ERR(rwsem_down_write_slowpath(sem, TASK_KILLABLE)))
return -EINTR;
} else {
rwsem_set_owner(sem);
}
return 0;
return __down_write_common(sem, TASK_KILLABLE);
}
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
tmp = RWSEM_UNLOCKED_VALUE;
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
RWSEM_WRITER_LOCKED)) {
rwsem_set_owner(sem);
return true;
}
return false;
return rwsem_write_trylock(sem);
}
/*
@ -1435,7 +1296,7 @@ static inline void __up_read(struct rw_semaphore *sem)
DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
RWSEM_FLAG_WAITERS)) {
clear_wr_nonspinnable(sem);
clear_nonspinnable(sem);
rwsem_wake(sem, tmp);
}
}
@ -1495,6 +1356,20 @@ void __sched down_read(struct rw_semaphore *sem)
}
EXPORT_SYMBOL(down_read);
int __sched down_read_interruptible(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_read_interruptible);
int __sched down_read_killable(struct rw_semaphore *sem)
{
might_sleep();
@ -1605,6 +1480,20 @@ void down_read_nested(struct rw_semaphore *sem, int subclass)
}
EXPORT_SYMBOL(down_read_nested);
int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_read_killable_nested);
void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
{
might_sleep();

51
lib/locking-selftest.c
View File

@ -58,10 +58,10 @@ static struct ww_mutex o, o2, o3;
* Normal standalone locks, for the circular and irq-context
* dependency tests:
*/
static DEFINE_RAW_SPINLOCK(lock_A);
static DEFINE_RAW_SPINLOCK(lock_B);
static DEFINE_RAW_SPINLOCK(lock_C);
static DEFINE_RAW_SPINLOCK(lock_D);
static DEFINE_SPINLOCK(lock_A);
static DEFINE_SPINLOCK(lock_B);
static DEFINE_SPINLOCK(lock_C);
static DEFINE_SPINLOCK(lock_D);
static DEFINE_RWLOCK(rwlock_A);
static DEFINE_RWLOCK(rwlock_B);
@ -93,12 +93,12 @@ static DEFINE_RT_MUTEX(rtmutex_D);
* but X* and Y* are different classes. We do this so that
* we do not trigger a real lockup:
*/
static DEFINE_RAW_SPINLOCK(lock_X1);
static DEFINE_RAW_SPINLOCK(lock_X2);
static DEFINE_RAW_SPINLOCK(lock_Y1);
static DEFINE_RAW_SPINLOCK(lock_Y2);
static DEFINE_RAW_SPINLOCK(lock_Z1);
static DEFINE_RAW_SPINLOCK(lock_Z2);
static DEFINE_SPINLOCK(lock_X1);
static DEFINE_SPINLOCK(lock_X2);
static DEFINE_SPINLOCK(lock_Y1);
static DEFINE_SPINLOCK(lock_Y2);
static DEFINE_SPINLOCK(lock_Z1);
static DEFINE_SPINLOCK(lock_Z2);
static DEFINE_RWLOCK(rwlock_X1);
static DEFINE_RWLOCK(rwlock_X2);
@ -138,10 +138,10 @@ static DEFINE_RT_MUTEX(rtmutex_Z2);
*/
#define INIT_CLASS_FUNC(class) \
static noinline void \
init_class_##class(raw_spinlock_t *lock, rwlock_t *rwlock, \
init_class_##class(spinlock_t *lock, rwlock_t *rwlock, \
struct mutex *mutex, struct rw_semaphore *rwsem)\
{ \
raw_spin_lock_init(lock); \
spin_lock_init(lock); \
rwlock_init(rwlock); \
mutex_init(mutex); \
init_rwsem(rwsem); \
@ -210,10 +210,10 @@ static void init_shared_classes(void)
* Shortcuts for lock/unlock API variants, to keep
* the testcases compact:
*/
#define L(x) raw_spin_lock(&lock_##x)
#define U(x) raw_spin_unlock(&lock_##x)
#define L(x) spin_lock(&lock_##x)
#define U(x) spin_unlock(&lock_##x)
#define LU(x) L(x); U(x)
#define SI(x) raw_spin_lock_init(&lock_##x)
#define SI(x) spin_lock_init(&lock_##x)
#define WL(x) write_lock(&rwlock_##x)
#define WU(x) write_unlock(&rwlock_##x)
@ -1341,7 +1341,7 @@ GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion3_soft_wlock)
#define I2(x) \
do { \
raw_spin_lock_init(&lock_##x); \
spin_lock_init(&lock_##x); \
rwlock_init(&rwlock_##x); \
mutex_init(&mutex_##x); \
init_rwsem(&rwsem_##x); \
@ -2005,10 +2005,23 @@ static void ww_test_edeadlk_acquire_wrong_slow(void)
static void ww_test_spin_nest_unlocked(void)
{
raw_spin_lock_nest_lock(&lock_A, &o.base);
spin_lock_nest_lock(&lock_A, &o.base);
U(A);
}
/* This is not a deadlock, because we have X1 to serialize Y1 and Y2 */
static void ww_test_spin_nest_lock(void)
{
spin_lock(&lock_X1);
spin_lock_nest_lock(&lock_Y1, &lock_X1);
spin_lock(&lock_A);
spin_lock_nest_lock(&lock_Y2, &lock_X1);
spin_unlock(&lock_A);
spin_unlock(&lock_Y2);
spin_unlock(&lock_Y1);
spin_unlock(&lock_X1);
}
static void ww_test_unneeded_slow(void)
{
WWAI(&t);
@ -2226,6 +2239,10 @@ static void ww_tests(void)
dotest(ww_test_spin_nest_unlocked, FAILURE, LOCKTYPE_WW);
pr_cont("\n");
print_testname("spinlock nest test");
dotest(ww_test_spin_nest_lock, SUCCESS, LOCKTYPE_WW);
pr_cont("\n");
printk(" -----------------------------------------------------\n");
printk(" |block | try |context|\n");
printk(" -----------------------------------------------------\n");