While fuzzing an arm64 kernel, Alexander Potapenko reported:
| BUG: KCSAN: data-race in ktime_get_mono_fast_ns / timekeeping_update
|
| write to 0xffffffc082e74248 of 56 bytes by interrupt on cpu 0:
| update_fast_timekeeper kernel/time/timekeeping.c:430 [inline]
| timekeeping_update+0x1d8/0x2d8 kernel/time/timekeeping.c:768
| timekeeping_advance+0x9e8/0xb78 kernel/time/timekeeping.c:2344
| update_wall_time+0x18/0x38 kernel/time/timekeeping.c:2360
| [...]
|
| read to 0xffffffc082e74258 of 8 bytes by task 5260 on cpu 1:
| __ktime_get_fast_ns kernel/time/timekeeping.c:372 [inline]
| ktime_get_mono_fast_ns+0x88/0x174 kernel/time/timekeeping.c:489
| init_srcu_struct_fields+0x40c/0x530 kernel/rcu/srcutree.c:263
| init_srcu_struct+0x14/0x20 kernel/rcu/srcutree.c:311
| [...]
|
| value changed: 0x000002f875d33266 -> 0x000002f877416866
|
| Reported by Kernel Concurrency Sanitizer on:
| CPU: 1 UID: 0 PID: 5260 Comm: syz.2.7483 Not tainted 6.12.0-rc3-dirty #78
This is a false positive data race between a seqcount latch writer and a reader
accessing stale data. Since its introduction, KCSAN has never understood the
seqcount_latch interface (due to being unannotated).
Unlike the regular seqlock interface, the seqcount_latch interface for latch
writers never has had a well-defined critical section, making it difficult to
teach tooling where the critical section starts and ends.
Introduce an instrumentable (non-raw) seqcount_latch interface, with
which we can clearly denote writer critical sections. This both helps
readability and tooling like KCSAN to understand when the writer is done
updating all latch copies.
Fixes: 88ecd153be ("seqlock, kcsan: Add annotations for KCSAN")
Reported-by: Alexander Potapenko <glider@google.com>
Co-developed-by: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Signed-off-by: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241104161910.780003-4-elver@google.com
When a remoteproc crashes or goes down unexpectedly this can result in
a state where locks held by the remoteproc will remain locked possibly
resulting in deadlock. This new API hwspin_lock_bust() allows
hwspinlock implementers to define a bust operation for freeing previously
acquired hwspinlocks after verifying ownership of the acquired lock.
Signed-off-by: Richard Maina <quic_rmaina@quicinc.com>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Chris Lew <quic_clew@quicinc.com>
Link: https://lore.kernel.org/r/20240529-hwspinlock-bust-v3-1-c8b924ffa5a2@quicinc.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
I have seen several cases of attempts to use mutex_unlock() to release an
object such that the object can then be freed by another task.
This is not safe because mutex_unlock(), in the
MUTEX_FLAG_WAITERS && !MUTEX_FLAG_HANDOFF case, accesses the mutex
structure after having marked it as unlocked; so mutex_unlock() requires
its caller to ensure that the mutex stays alive until mutex_unlock()
returns.
If MUTEX_FLAG_WAITERS is set and there are real waiters, those waiters
have to keep the mutex alive, but we could have a spurious
MUTEX_FLAG_WAITERS left if an interruptible/killable waiter bailed
between the points where __mutex_unlock_slowpath() did the cmpxchg
reading the flags and where it acquired the wait_lock.
( With spinlocks, that kind of code pattern is allowed and, from what I
remember, used in several places in the kernel. )
Document this, such a semantic difference between mutexes and spinlocks
is fairly unintuitive.
[ mingo: Made the changelog a bit more assertive, refined the comments. ]
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231130204817.2031407-1-jannh@google.com
Use capital letters in acronyms for CD-ROM, FPGA, and PCMCIA.
Use capital letter in the first word of chapter headings for
Locking, Timers, and "Brief tutorial on CRC computation".
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Moritz Fischer <mdf@kernel.org>
Cc: Wu Hao <hao.wu@intel.com>
Cc: Tom Rix <trix@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Reviewed-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20230516001518.14514-1-rdunlap@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The config is actually called CONFIG_RT_MUTEXES, not CONFIG_RT_MUTEX.
The config CONFIG_LOCK_TORTURE_TEST should be connected by underscore, for
the sake of consistent referencing to configs in the kernel documentation.
Address those issues.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20230220165749.12850-1-lukas.bulwahn@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Unless it was duplicate on purpose, to emphasize that a raw_spinlock_t
is always a spinning lock regardless of PREEMPT_RT or kernel config,
it's a bit odd that this text is duplicate. So, this patch just clean
it up, keeping the consistency with the other sections of the text.
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 919e9e6395 ("Documentation: Add lock ordering and nesting documentation")
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Link: https://lore.kernel.org/r/20220321144133.49804-1-gpiccoli@igalia.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
With PREEMPT_RT the _bh() version of a spinlock leaves preemption
enabled, align the doc to say that instead of the opposite.
Reported-by: Leah Leshchinsky <lleshchi@redhat.com>
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20220224212312.2601153-1-ahalaney@redhat.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The initial implementation of migrate_disable() for mainline was a
wrapper around preempt_disable(). RT kernels substituted this with
a real migrate disable implementation.
Later on mainline gained true migrate disable support, but the
documentation was not updated.
Update the documentation, remove the claims about migrate_disable()
mapping to preempt_disable() on non-PREEMPT_RT kernels.
Fixes: 74d862b682 ("sched: Make migrate_disable/enable() independent of RT")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211127163200.10466-2-bigeasy@linutronix.de
The previous commits do exactly what this entry in the TODO file asks
for, thus we can remove it now as it is no longer applicable.
Signed-off-by: Fernando Ramos <greenfoo@u92.eu>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210924064324.229457-18-greenfoo@u92.eu
This patch fixes file references from txt to rst file ending in
ww-mutex-design.rst and futex-requeue-pi.rst. While on it fix a spelling
issue "desgin" to "design" reported by Matthew Wilcox.
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20210823183143.1691344-1-aahringo@redhat.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The block condition matrix is using 'E' as the writer notation,
however, the writer reminder below the matrix is using 'W', to make
them consistent and make the matrix more readable, we'd better to use
'W' to represent writer.
Suggested-by: Waiman Long <llong@redhat.com>
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lkml.kernel.org/r/1621868745-23311-1-git-send-email-sxwjean@me.com
Sequence counters with an associated write serialization lock are called
seqcount_LOCKNAME_t. Fix the documentation accordingly.
While at it, remove a paragraph that inappropriately discussed a
seqlock.h implementation detail.
Fixes: 6dd699b13d ("seqlock: seqcount_LOCKNAME_t: Standardize naming convention")
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20201206162143.14387-2-a.darwish@linutronix.de
There are several warnings caused by a recent change
224ec489d3 ("lockdep/Documention: Recursive read lock detection reasoning")
Those are reported by htmldocs build:
Documentation/locking/lockdep-design.rst:429: WARNING: Definition list ends without a blank line; unexpected unindent.
Documentation/locking/lockdep-design.rst:452: WARNING: Block quote ends without a blank line; unexpected unindent.
Documentation/locking/lockdep-design.rst:453: WARNING: Unexpected indentation.
Documentation/locking/lockdep-design.rst:453: WARNING: Blank line required after table.
Documentation/locking/lockdep-design.rst:454: WARNING: Block quote ends without a blank line; unexpected unindent.
Documentation/locking/lockdep-design.rst:455: WARNING: Unexpected indentation.
Documentation/locking/lockdep-design.rst:455: WARNING: Blank line required after table.
Documentation/locking/lockdep-design.rst:456: WARNING: Block quote ends without a blank line; unexpected unindent.
Documentation/locking/lockdep-design.rst:457: WARNING: Unexpected indentation.
Documentation/locking/lockdep-design.rst:457: WARNING: Blank line required after table.
Besides the reported issues, there are some missing blank
lines that ended producing wrong html output, and some
literals are not properly identified.
Also, the symbols used at the irq enabled/disable table
are not displayed as expected, as they're not literals.
Also, on another table they're using a different notation.
Fixes: 224ec489d3 ("lockdep/Documention: Recursive read lock detection reasoning")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/3b9431ac5c01e38111cd59928a93e7259ab7db0f.1603791716.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Latch sequence counters are a multiversion concurrency control mechanism
where the seqcount_t counter even/odd value is used to switch between
two copies of protected data. This allows the seqcount_t read path to
safely interrupt its write side critical section (e.g. from NMIs).
Initially, latch sequence counters were implemented as a single write
function above plain seqcount_t: raw_write_seqcount_latch(). The read
side was expected to use plain seqcount_t raw_read_seqcount().
A specialized latch read function, raw_read_seqcount_latch(), was later
added. It became the standardized way for latch read paths. Due to the
dependent load, it has one read memory barrier less than the plain
seqcount_t raw_read_seqcount() API.
Only raw_write_seqcount_latch() and raw_read_seqcount_latch() should be
used with latch sequence counters. Having *unique* read and write path
APIs means that latch sequence counters are actually a data type of
their own -- just inappropriately overloading plain seqcount_t.
Introduce seqcount_latch_t. This adds type-safety and ensures that only
the correct latch-safe APIs are to be used.
Not to break bisection, let the latch APIs also accept plain seqcount_t
or seqcount_raw_spinlock_t. After converting all call sites to
seqcount_latch_t, only that new data type will be allowed.
References: 9b0fd802e8 ("seqcount: Add raw_write_seqcount_latch()")
References: 7fc26327b7 ("seqlock: Introduce raw_read_seqcount_latch()")
References: aadd6e5caa ("time/sched_clock: Use raw_read_seqcount_latch()")
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200827114044.11173-4-a.darwish@linutronix.de
This patch add the documentation piece for the reasoning of deadlock
detection related to recursive read lock. The following sections are
added:
* Explain what is a recursive read lock, and what deadlock cases
they could introduce.
* Introduce the notations for different types of dependencies, and
the definition of strong paths.
* Proof for a closed strong path is both sufficient and necessary
for deadlock detections with recursive read locks involved. The
proof could also explain why we call the path "strong"
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-3-boqun.feng@gmail.com
Fix issues with local_locks documentation:
- fix function names, local_lock.h has local_unlock_irqrestore(), not
local_lock_irqrestore()
- fix mapping table, local_unlock_irqrestore() maps to
local_irq_restore(), not _save()
Signed-off-by: Marta Rybczynska <rybczynska@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/CAApg2=SKxQ3Sqwj6TZnV-0x0cKLXFKDaPvXT4N15MPDMKq724g@mail.gmail.com
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Merge tag 'docs-5.9-2' of git://git.lwn.net/linux
Pull documentation fixes from Jonathan Corbet:
"A handful of obvious fixes that wandered in during the merge window"
* tag 'docs-5.9-2' of git://git.lwn.net/linux:
Documentation/locking/locktypes: fix the typo
doc/zh_CN: resolve undefined label warning in admin-guide index
doc/zh_CN: fix title heading markup in admin-guide cpu-load
docs: remove the 2.6 "Upgrading I2C Drivers" guide
docs: Correct the release date of 5.2 stable
mailmap: Update comments for with format and more detalis
docs: cdrom: Fix a typo and rst markup
Doc: admin-guide: use correct legends in kernel-parameters.txt
Documentation/features: refresh RISC-V arch support files
documentation: coccinelle: Improve command example for make C={1,2}
Core-api: Documentation: Replace deprecated :c:func: Usage
Dev-tools: Documentation: Replace deprecated :c:func: Usage
Filesystems: Documentation: Replace deprecated :c:func: Usage
docs: trace: fix a typo
- Untangle the header spaghetti which causes build failures in various
situations caused by the lockdep additions to seqcount to validate that
the write side critical sections are non-preemptible.
- The seqcount associated lock debug addons which were blocked by the
above fallout.
seqcount writers contrary to seqlock writers must be externally
serialized, which usually happens via locking - except for strict per
CPU seqcounts. As the lock is not part of the seqcount, lockdep cannot
validate that the lock is held.
This new debug mechanism adds the concept of associated locks.
sequence count has now lock type variants and corresponding
initializers which take a pointer to the associated lock used for
writer serialization. If lockdep is enabled the pointer is stored and
write_seqcount_begin() has a lockdep assertion to validate that the
lock is held.
Aside of the type and the initializer no other code changes are
required at the seqcount usage sites. The rest of the seqcount API is
unchanged and determines the type at compile time with the help of
_Generic which is possible now that the minimal GCC version has been
moved up.
Adding this lockdep coverage unearthed a handful of seqcount bugs which
have been addressed already independent of this.
While generaly useful this comes with a Trojan Horse twist: On RT
kernels the write side critical section can become preemtible if the
writers are serialized by an associated lock, which leads to the well
known reader preempts writer livelock. RT prevents this by storing the
associated lock pointer independent of lockdep in the seqcount and
changing the reader side to block on the lock when a reader detects
that a writer is in the write side critical section.
- Conversion of seqcount usage sites to associated types and initializers.
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Merge tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Thomas Gleixner:
"A set of locking fixes and updates:
- Untangle the header spaghetti which causes build failures in
various situations caused by the lockdep additions to seqcount to
validate that the write side critical sections are non-preemptible.
- The seqcount associated lock debug addons which were blocked by the
above fallout.
seqcount writers contrary to seqlock writers must be externally
serialized, which usually happens via locking - except for strict
per CPU seqcounts. As the lock is not part of the seqcount, lockdep
cannot validate that the lock is held.
This new debug mechanism adds the concept of associated locks.
sequence count has now lock type variants and corresponding
initializers which take a pointer to the associated lock used for
writer serialization. If lockdep is enabled the pointer is stored
and write_seqcount_begin() has a lockdep assertion to validate that
the lock is held.
Aside of the type and the initializer no other code changes are
required at the seqcount usage sites. The rest of the seqcount API
is unchanged and determines the type at compile time with the help
of _Generic which is possible now that the minimal GCC version has
been moved up.
Adding this lockdep coverage unearthed a handful of seqcount bugs
which have been addressed already independent of this.
While generally useful this comes with a Trojan Horse twist: On RT
kernels the write side critical section can become preemtible if
the writers are serialized by an associated lock, which leads to
the well known reader preempts writer livelock. RT prevents this by
storing the associated lock pointer independent of lockdep in the
seqcount and changing the reader side to block on the lock when a
reader detects that a writer is in the write side critical section.
- Conversion of seqcount usage sites to associated types and
initializers"
* tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (25 commits)
locking/seqlock, headers: Untangle the spaghetti monster
locking, arch/ia64: Reduce <asm/smp.h> header dependencies by moving XTP bits into the new <asm/xtp.h> header
x86/headers: Remove APIC headers from <asm/smp.h>
seqcount: More consistent seqprop names
seqcount: Compress SEQCNT_LOCKNAME_ZERO()
seqlock: Fold seqcount_LOCKNAME_init() definition
seqlock: Fold seqcount_LOCKNAME_t definition
seqlock: s/__SEQ_LOCKDEP/__SEQ_LOCK/g
hrtimer: Use sequence counter with associated raw spinlock
kvm/eventfd: Use sequence counter with associated spinlock
userfaultfd: Use sequence counter with associated spinlock
NFSv4: Use sequence counter with associated spinlock
iocost: Use sequence counter with associated spinlock
raid5: Use sequence counter with associated spinlock
vfs: Use sequence counter with associated spinlock
timekeeping: Use sequence counter with associated raw spinlock
xfrm: policy: Use sequence counters with associated lock
netfilter: nft_set_rbtree: Use sequence counter with associated rwlock
netfilter: conntrack: Use sequence counter with associated spinlock
sched: tasks: Use sequence counter with associated spinlock
...
while to come. Changes include:
- Some new Chinese translations
- Progress on the battle against double words words and non-HTTPS URLs
- Some block-mq documentation
- More RST conversions from Mauro. At this point, that task is
essentially complete, so we shouldn't see this kind of churn again for a
while. Unless we decide to switch to asciidoc or something...:)
- Lots of typo fixes, warning fixes, and more.
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Merge tag 'docs-5.9' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"It's been a busy cycle for documentation - hopefully the busiest for a
while to come. Changes include:
- Some new Chinese translations
- Progress on the battle against double words words and non-HTTPS
URLs
- Some block-mq documentation
- More RST conversions from Mauro. At this point, that task is
essentially complete, so we shouldn't see this kind of churn again
for a while. Unless we decide to switch to asciidoc or
something...:)
- Lots of typo fixes, warning fixes, and more"
* tag 'docs-5.9' of git://git.lwn.net/linux: (195 commits)
scripts/kernel-doc: optionally treat warnings as errors
docs: ia64: correct typo
mailmap: add entry for <alobakin@marvell.com>
doc/zh_CN: add cpu-load Chinese version
Documentation/admin-guide: tainted-kernels: fix spelling mistake
MAINTAINERS: adjust kprobes.rst entry to new location
devices.txt: document rfkill allocation
PCI: correct flag name
docs: filesystems: vfs: correct flag name
docs: filesystems: vfs: correct sync_mode flag names
docs: path-lookup: markup fixes for emphasis
docs: path-lookup: more markup fixes
docs: path-lookup: fix HTML entity mojibake
CREDITS: Replace HTTP links with HTTPS ones
docs: process: Add an example for creating a fixes tag
doc/zh_CN: add Chinese translation prefer section
doc/zh_CN: add clearing-warn-once Chinese version
doc/zh_CN: add admin-guide index
doc:it_IT: process: coding-style.rst: Correct __maybe_unused compiler label
futex: MAINTAINERS: Re-add selftests directory
...
- LKMM updates: mostly documentation changes, but also some new litmus tests for atomic ops.
- KCSAN updates: the most important change is that GCC 11 now has all fixes in place
to support KCSAN, so GCC support can be enabled again. Also more annotations.
- futex updates: minor cleanups and simplifications
- seqlock updates: merge preparatory changes/cleanups for the 'associated locks' facilities.
- lockdep updates:
- simplify IRQ trace event handling
- add various new debug checks
- simplify header dependencies, split out <linux/lockdep_types.h>, decouple
lockdep from other low level headers some more
- fix NMI handling
- misc cleanups and smaller fixes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
- LKMM updates: mostly documentation changes, but also some new litmus
tests for atomic ops.
- KCSAN updates: the most important change is that GCC 11 now has all
fixes in place to support KCSAN, so GCC support can be enabled again.
Also more annotations.
- futex updates: minor cleanups and simplifications
- seqlock updates: merge preparatory changes/cleanups for the
'associated locks' facilities.
- lockdep updates:
- simplify IRQ trace event handling
- add various new debug checks
- simplify header dependencies, split out <linux/lockdep_types.h>,
decouple lockdep from other low level headers some more
- fix NMI handling
- misc cleanups and smaller fixes
* tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (60 commits)
kcsan: Improve IRQ state trace reporting
lockdep: Refactor IRQ trace events fields into struct
seqlock: lockdep assert non-preemptibility on seqcount_t write
lockdep: Add preemption enabled/disabled assertion APIs
seqlock: Implement raw_seqcount_begin() in terms of raw_read_seqcount()
seqlock: Add kernel-doc for seqcount_t and seqlock_t APIs
seqlock: Reorder seqcount_t and seqlock_t API definitions
seqlock: seqcount_t latch: End read sections with read_seqcount_retry()
seqlock: Properly format kernel-doc code samples
Documentation: locking: Describe seqlock design and usage
locking/qspinlock: Do not include atomic.h from qspinlock_types.h
locking/atomic: Move ATOMIC_INIT into linux/types.h
lockdep: Move list.h inclusion into lockdep.h
locking/lockdep: Fix TRACE_IRQFLAGS vs. NMIs
futex: Remove unused or redundant includes
futex: Consistently use fshared as boolean
futex: Remove needless goto's
futex: Remove put_futex_key()
rwsem: fix commas in initialisation
docs: locking: Replace HTTP links with HTTPS ones
...
A sequence counter write side critical section must be protected by some
form of locking to serialize writers. If the serialization primitive is
not disabling preemption implicitly, preemption has to be explicitly
disabled before entering the write side critical section.
There is no built-in debugging mechanism to verify that the lock used
for writer serialization is held and preemption is disabled. Some usage
sites like dma-buf have explicit lockdep checks for the writer-side
lock, but this covers only a small portion of the sequence counter usage
in the kernel.
Add new sequence counter types which allows to associate a lock to the
sequence counter at initialization time. The seqcount API functions are
extended to provide appropriate lockdep assertions depending on the
seqcount/lock type.
For sequence counters with associated locks that do not implicitly
disable preemption, preemption protection is enforced in the sequence
counter write side functions. This removes the need to explicitly add
preempt_disable/enable() around the write side critical sections: the
write_begin/end() functions for these new sequence counter types
automatically do this.
Introduce the following seqcount types with associated locks:
seqcount_spinlock_t
seqcount_raw_spinlock_t
seqcount_rwlock_t
seqcount_mutex_t
seqcount_ww_mutex_t
Extend the seqcount read and write functions to branch out to the
specific seqcount_LOCKTYPE_t implementation at compile-time. This avoids
kernel API explosion per each new seqcount_LOCKTYPE_t added. Add such
compile-time type detection logic into a new, internal, seqlock header.
Document the proper seqcount_LOCKTYPE_t usage, and rationale, at
Documentation/locking/seqlock.rst.
If lockdep is disabled, this lock association is compiled out and has
neither storage size nor runtime overhead.
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-10-a.darwish@linutronix.de
Proper documentation for the design and usage of sequence counters and
sequential locks does not exist. Complete the seqlock.h documentation as
follows:
- Divide all documentation on a seqcount_t vs. seqlock_t basis. The
description for both mechanisms was intermingled, which is incorrect
since the usage constrains for each type are vastly different.
- Add an introductory paragraph describing the internal design of, and
rationale for, sequence counters.
- Document seqcount_t writer non-preemptibility requirement, which was
not previously documented anywhere, and provide a clear rationale.
- Provide template code for seqcount_t and seqlock_t initialization
and reader/writer critical sections.
- Recommend using seqlock_t by default. It implicitly handles the
serialization and non-preemptibility requirements of writers.
At seqlock.h:
- Remove references to brlocks as they've long been removed from the
kernel.
- Remove references to gcc-3.x since the kernel's minimum supported
gcc version is 4.9.
References: 0f6ed63b17 ("no need to keep brlock macros anymore...")
References: 6ec4476ac8 ("Raise gcc version requirement to 4.9")
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-2-a.darwish@linutronix.de
Rationale:
Reduces attack surface on kernel devs opening the links for MITM
as HTTPS traffic is much harder to manipulate.
Deterministic algorithm:
For each file:
If not .svg:
For each line:
If doesn't contain `\bxmlns\b`:
For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`:
If neither `\bgnu\.org/license`, nor `\bmozilla\.org/MPL\b`:
If both the HTTP and HTTPS versions
return 200 OK and serve the same content:
Replace HTTP with HTTPS.
Signed-off-by: Alexander A. Klimov <grandmaster@al2klimov.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200713115728.33905-1-grandmaster@al2klimov.de
Drop the doubled word "up".
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200703213649.30948-3-rdunlap@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Change the phrase "at at least" to "to at least" to be more
readable.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200703213649.30948-2-rdunlap@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Rationale:
Reduces attack surface on kernel devs opening the links for MITM
as HTTPS traffic is much harder to manipulate.
Deterministic algorithm:
For each file:
If not .svg:
For each line:
If doesn't contain `\bxmlns\b`:
For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`:
If neither `\bgnu\.org/license`, nor `\bmozilla\.org/MPL\b`:
If both the HTTP and HTTPS versions
return 200 OK and serve the same content:
Replace HTTP with HTTPS.
Signed-off-by: Alexander A. Klimov <grandmaster@al2klimov.de>
Link: https://lore.kernel.org/r/20200713115728.33905-1-grandmaster@al2klimov.de
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
- Add a SPDX header;
- Adjust document and section titles;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add it to RCU/index.rst.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
set from Mauro toward the completion of the RST conversion. I *really*
hope we are getting close to the end of this. Meanwhile, those patches
reach pretty far afield to update document references around the tree;
there should be no actual code changes there. There will be, alas, more of
the usual trivial merge conflicts.
Beyond that we have more translations, improvements to the sphinx
scripting, a number of additions to the sysctl documentation, and lots of
fixes.
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Merge tag 'docs-5.8' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"A fair amount of stuff this time around, dominated by yet another
massive set from Mauro toward the completion of the RST conversion. I
*really* hope we are getting close to the end of this. Meanwhile,
those patches reach pretty far afield to update document references
around the tree; there should be no actual code changes there. There
will be, alas, more of the usual trivial merge conflicts.
Beyond that we have more translations, improvements to the sphinx
scripting, a number of additions to the sysctl documentation, and lots
of fixes"
* tag 'docs-5.8' of git://git.lwn.net/linux: (130 commits)
Documentation: fixes to the maintainer-entry-profile template
zswap: docs/vm: Fix typo accept_threshold_percent in zswap.rst
tracing: Fix events.rst section numbering
docs: acpi: fix old http link and improve document format
docs: filesystems: add info about efivars content
Documentation: LSM: Correct the basic LSM description
mailmap: change email for Ricardo Ribalda
docs: sysctl/kernel: document unaligned controls
Documentation: admin-guide: update bug-hunting.rst
docs: sysctl/kernel: document ngroups_max
nvdimm: fixes to maintainter-entry-profile
Documentation/features: Correct RISC-V kprobes support entry
Documentation/features: Refresh the arch support status files
Revert "docs: sysctl/kernel: document ngroups_max"
docs: move locking-specific documents to locking/
docs: move digsig docs to the security book
docs: move the kref doc into the core-api book
docs: add IRQ documentation at the core-api book
docs: debugging-via-ohci1394.txt: add it to the core-api book
docs: fix references for ipmi.rst file
...
preempt_disable() and local_irq_disable/save() are in principle per CPU big
kernel locks. This has several downsides:
- The protection scope is unknown
- Violation of protection rules is hard to detect by instrumentation
- For PREEMPT_RT such sections, unless in low level critical code, can
violate the preemptability constraints.
To address this PREEMPT_RT introduced the concept of local_locks which are
strictly per CPU.
The lock operations map to preempt_disable(), local_irq_disable/save() and
the enabling counterparts on non RT enabled kernels.
If lockdep is enabled local locks gain a lock map which tracks the usage
context. This will catch cases where an area is protected by
preempt_disable() but the access also happens from interrupt context. local
locks have identified quite a few such issues over the years, the most
recent example is:
b7d5dc2107 ("random: add a spinlock_t to struct batched_entropy")
Aside of the lockdep coverage this also improves code readability as it
precisely annotates the protection scope.
PREEMPT_RT substitutes these local locks with 'sleeping' spinlocks to
protect such sections while maintaining preemtability and CPU locality.
local locks can replace:
- preempt_enable()/disable() pairs
- local_irq_disable/enable() pairs
- local_irq_save/restore() pairs
They are also used to replace code which implicitly disables preemption
like:
- get_cpu()/put_cpu()
- get_cpu_var()/put_cpu_var()
with PREEMPT_RT friendly constructs.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-2-bigeasy@linutronix.de
Minor editorial fixes:
- remove 'enabled' from PREEMPT_RT enabled kernels for consistency
- add some periods for consistency
- add "'" for possessive CPU's
- spell out interrupts
[ tglx: Picked up Paul's suggestions ]
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lkml.kernel.org/r/ac615f36-0b44-408d-aeab-d76e4241add4@infradead.org
The documentation of rw_semaphores is wrong as it claims that the non-owner
reader release is not supported by RT. That's just history biased memory
distortion.
Split the 'Owner semantics' section up and add separate sections for
semaphore and rw_semaphore to reflect reality.
Aside of that the following updates are done:
- Add pseudo code to document the spinlock state preserving mechanism on
PREEMPT_RT
- Wordsmith the bitspinlock and lock nesting sections
Co-developed-by: Paul McKenney <paulmck@kernel.org>
Signed-off-by: Paul McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lkml.kernel.org/r/87wo78y5yy.fsf@nanos.tec.linutronix.de
The kernel provides a variety of locking primitives. The nesting of these
lock types and the implications of them on RT enabled kernels is nowhere
documented.
Add initial documentation.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113242.026561244@linutronix.de
Commit 2e4f5382d1 ("locking/doc: Rename LOCK/UNLOCK to
ACQUIRE/RELEASE") has not appied to 'spinlock.rst'. This commit updates
the doc for the change.
Signed-off-by: SeongJae Park <sjpark@amazon.com>
Link: https://lore.kernel.org/r/20200131205237.29535-2-sj38.park@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Remove the clever example about read-write lock because this type of
lock is not recommended anymore (according to the very same document).
So there is no reason to teach clever things that people should not do.
Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Some files got renamed but probably due to some merge conflicts,
a few references still point to the old locations.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Convert the locking documents to ReST and add them to the
kernel development book where it belongs.
Most of the stuff here is just to make Sphinx to properly
parse the text file, as they're already in good shape,
not requiring massive changes in order to be parsed.
The conversion is actually:
- add blank lines and identation in order to identify paragraphs;
- fix tables markups;
- add some lists markups;
- mark literal blocks;
- adjust title markups.
At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Federico Vaga <federico.vaga@vaga.pv.it>
More words are added to lockdep design document regarding key concepts,
which should help people without lockdep experience read and understand
lockdep reports.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-3-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Since the removal of FS_RECLAIM annotations, lockdep states contain four
characters, not six.
Fixes: e5684bbfc3 ("Documentation/locking/lockdep: Update info about states")
Fixes: d92a8cfcb3 ("locking/lockdep: Rework FS_RECLAIM annotation")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
readability improvements for the formatted output, some LICENSES updates
including the addition of the ISC license, the removal of the unloved and
unmaintained 00-INDEX files, the deprecated APIs document from Kees, more
MM docs from Mike Rapoport, and the usual pile of typo fixes and
corrections.
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Merge tag 'docs-4.20' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"This is a fairly typical cycle for documentation. There's some welcome
readability improvements for the formatted output, some LICENSES
updates including the addition of the ISC license, the removal of the
unloved and unmaintained 00-INDEX files, the deprecated APIs document
from Kees, more MM docs from Mike Rapoport, and the usual pile of typo
fixes and corrections"
* tag 'docs-4.20' of git://git.lwn.net/linux: (41 commits)
docs: Fix typos in histogram.rst
docs: Introduce deprecated APIs list
kernel-doc: fix declaration type determination
doc: fix a typo in adding-syscalls.rst
docs/admin-guide: memory-hotplug: remove table of contents
doc: printk-formats: Remove bogus kobject references for device nodes
Documentation: preempt-locking: Use better example
dm flakey: Document "error_writes" feature
docs/completion.txt: Fix a couple of punctuation nits
LICENSES: Add ISC license text
LICENSES: Add note to CDDL-1.0 license that it should not be used
docs/core-api: memory-hotplug: add some details about locking internals
docs/core-api: rename memory-hotplug-notifier to memory-hotplug
docs: improve readability for people with poorer eyesight
yama: clarify ptrace_scope=2 in Yama documentation
docs/vm: split memory hotplug notifier description to Documentation/core-api
docs: move memory hotplug description into admin-guide/mm
doc: Fix acronym "FEKEK" in ecryptfs
docs: fix some broken documentation references
iommu: Fix passthrough option documentation
...
Fix incorrect line number in example output
Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Cc: Jiri Kosina <trivial@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/1538391663-54524-1-git-send-email-andrew.murray@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
