SRCU:
- Introduction of the new SRCU-lite flavour with a new pair of
srcu_read_[un]lock_lite() APIs. In practice the read side using
this flavour becomes lighter by removing a full memory barrier on
LOCK and a full memory barrier on UNLOCK. This comes at the
expense of a higher latency write side with two (in the best case
of a snaphot of unused read-sides) or more RCU grace periods on
the update side which now assumes by itself the whole full
ordering guarantee against the LOCK/UNLOCK counters on both
indexes, along with the accesses performed inside.
Uretprobes is a known potential user.
Note this doesn't replace the default normal flavour of SRCU which
still behaves the same as usual.
- Add testing of SRCU-lite through rcutorture and rcuscale
- Various cleanups on the way.
FIXES:
- Allow short-circuiting RCU-TASKS-RUDE grace periods on architectures
that have sane noinstr boundaries forbidding tracing on low-level
idle and kernel entry code. RCU-TASKS is enough on such configurations
because it involves an RCU grace period that waits for all idle
tasks to either schedule out voluntarily or enter into RCU
unwatched noinstr code.
- Allow and test start_poll_synchronize_rcu() with IRQs disabled.
- Mention rcuog kthreads in relevant documentation and Kconfig help
- Various fixes and consolidations
RCUTORTURE:
- Add --no-affinity on tools to leave the affinity setting of guests
up to the user.
- Add guest_os_delay parameter to rcuscale for better warm-up
control.
- Fix and improve some rcuscale error handling.
- Various cleanups and fixes
STALL:
- Remove dead code
- Stop dumping tasks if a stalled grace period eventually ended
midway as that only produces confusing output.
- Optimize detection of stalling CPUs and avoid useless node
locking otherwise.
NOCB:
- Fix rcu_barrier() hang due to a race against callbacks
deoffloading. This is not yet used, except by rcutorture, and
waits for its promised cpusets interface.
- Remove leftover function declaration
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Merge tag 'rcu.release.v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux
Pull RCU updates from Frederic Weisbecker:
"SRCU:
- Introduction of the new SRCU-lite flavour with a new pair of
srcu_read_[un]lock_lite() APIs. In practice the read side using
this flavour becomes lighter by removing a full memory barrier on
LOCK and a full memory barrier on UNLOCK. This comes at the expense
of a higher latency write side with two (in the best case of a
snaphot of unused read-sides) or more RCU grace periods on the
update side which now assumes by itself the whole full ordering
guarantee against the LOCK/UNLOCK counters on both indexes, along
with the accesses performed inside.
Uretprobes is a known potential user.
Note this doesn't replace the default normal flavour of SRCU which
still behaves the same as usual.
- Add testing of SRCU-lite through rcutorture and rcuscale
- Various cleanups on the way.
Fixes:
- Allow short-circuiting RCU-TASKS-RUDE grace periods on
architectures that have sane noinstr boundaries forbidding tracing
on low-level idle and kernel entry code. RCU-TASKS is enough on
such configurations because it involves an RCU grace period that
waits for all idle tasks to either schedule out voluntarily or
enter into RCU unwatched noinstr code.
- Allow and test start_poll_synchronize_rcu() with IRQs disabled.
- Mention rcuog kthreads in relevant documentation and Kconfig help
- Various fixes and consolidations
rcutorture:
- Add --no-affinity on tools to leave the affinity setting of guests
up to the user.
- Add guest_os_delay parameter to rcuscale for better warm-up
control.
- Fix and improve some rcuscale error handling.
- Various cleanups and fixes
stall:
- Remove dead code
- Stop dumping tasks if a stalled grace period eventually ended
midway as that only produces confusing output.
- Optimize detection of stalling CPUs and avoid useless node locking
otherwise.
NOCB:
- Fix rcu_barrier() hang due to a race against callbacks
deoffloading. This is not yet used, except by rcutorture, and waits
for its promised cpusets interface.
- Remove leftover function declaration"
* tag 'rcu.release.v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (42 commits)
rcuscale: Remove redundant WARN_ON_ONCE() splat
rcuscale: Do a proper cleanup if kfree_scale_init() fails
srcu: Unconditionally record srcu_read_lock_lite() in ->srcu_reader_flavor
srcu: Check for srcu_read_lock_lite() across all CPUs
srcu: Remove smp_mb() from srcu_read_unlock_lite()
rcutorture: Avoid printing cpu=-1 for no-fault RCU boost failure
rcuscale: Add guest_os_delay module parameter
refscale: Correct affinity check
torture: Add --no-affinity parameter to kvm.sh
rcu/nocb: Fix missed RCU barrier on deoffloading
rcu/kvfree: Fix data-race in __mod_timer / kvfree_call_rcu
rcu/srcutiny: don't return before reenabling preemption
rcu-tasks: Remove open-coded one-byte cmpxchg() emulation
doc: Remove kernel-parameters.txt entry for rcutorture.read_exit
rcutorture: Test start-poll primitives with interrupts disabled
rcu: Permit start_poll_synchronize_rcu*() with interrupts disabled
rcu: Allow short-circuiting of synchronize_rcu_tasks_rude()
doc: Add rcuog kthreads to kernel-per-CPU-kthreads.rst
rcu: Add rcuog kthreads to RCU_NOCB_CPU help text
rcu: Use the BITS_PER_LONG macro
...
There are two places where WARN_ON_ONCE() is called two times
in the error paths. One which is encapsulated into if() condition
and another one, which is unnecessary, is placed in the brackets.
Remove an extra WARN_ON_ONCE() splat which is in brackets.
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
A static analyzer for C, Smatch, reports and triggers below
warnings:
kernel/rcu/rcuscale.c:1215 rcu_scale_init()
warn: inconsistent returns 'global &fullstop_mutex'.
The checker complains about, we do not unlock the "fullstop_mutex"
mutex, in case of hitting below error path:
<snip>
...
if (WARN_ON_ONCE(jiffies_at_lazy_cb - jif_start < 2 * HZ)) {
pr_alert("ERROR: call_rcu() CBs are not being lazy as expected!\n");
WARN_ON_ONCE(1);
return -1;
^^^^^^^^^^
...
<snip>
it happens because "-1" is returned right away instead of
doing a proper unwinding.
Fix it by jumping to "unwind" label instead of returning -1.
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Closes: https://lore.kernel.org/rcu/ZxfTrHuEGtgnOYWp@pc636/T/
Fixes: 084e04fff1 ("rcuscale: Add laziness and kfree tests")
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Currently, srcu_read_lock_lite() uses the SRCU_READ_FLAVOR_LITE bit in
->srcu_reader_flavor to communicate to the grace-period processing in
srcu_readers_active_idx_check() that the smp_mb() must be replaced by a
synchronize_rcu(). Unfortunately, ->srcu_reader_flavor is not updated
unless the kernel is built with CONFIG_PROVE_RCU=y. Therefore in all
kernels built with CONFIG_PROVE_RCU=n, srcu_readers_active_idx_check()
incorrectly uses smp_mb() instead of synchronize_rcu() for srcu_struct
structures whose readers use srcu_read_lock_lite().
This commit therefore causes Tree SRCU srcu_read_lock_lite()
to unconditionally update ->srcu_reader_flavor so that
srcu_readers_active_idx_check() can make the correct choice.
Reported-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Closes: https://lore.kernel.org/all/d07e8f4a-d5ff-4c8e-8e61-50db285c57e9@amd.com/
Fixes: c0f08d6b5a61 ("srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite()")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
If srcu_read_lock_lite() is used on a given srcu_struct structure, then
the grace-period processing must do synchronize_rcu() instead of smp_mb()
between the scans of the ->srcu_unlock_count[] and ->srcu_lock_count[]
counters. Currently, it does that by testing the SRCU_READ_FLAVOR_LITE
bit of the ->srcu_reader_flavor mask, which works well. But only if
the CPU running that srcu_struct structure's grace period has previously
executed srcu_read_lock_lite(), which might not be the case, especially
just after that srcu_struct structure has been created and initialized.
This commit therefore updates the srcu_readers_unlock_idx() function
to OR together the ->srcu_reader_flavor masks from all CPUs, and
then make the srcu_readers_active_idx_check() function that test the
SRCU_READ_FLAVOR_LITE bit in the resulting mask.
Note that the srcu_readers_unlock_idx() function is already scanning all
the CPUs to sum up the ->srcu_unlock_count[] fields and that this is on
the grace-period slow path, hence no concerns about the small amount of
extra work.
Reported-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Closes: https://lore.kernel.org/all/d07e8f4a-d5ff-4c8e-8e61-50db285c57e9@amd.com/
Fixes: c0f08d6b5a61 ("srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite()")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
If a CPU runs throughout the stalled grace period without passing
through a quiescent state, RCU priority boosting cannot help.
The rcu_torture_boost_failed() function therefore prints a message
flagging the first such CPU. However, if the stall was instead due to
(for example) RCU's grace-period kthread being starved of CPU, there will
be no such CPU, causing rcu_check_boost_fail() to instead pass back -1
through its cpup CPU-pointer parameter.
Therefore, the current message complains about a mythical CPU -1.
This commit therefore checks for this situation, and notes that all CPUs
have passed through a quiescent state.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit adds a guest_os_delay module parameter that extends warm-up
and cool-down the specified number of seconds before and after the series
of test runs. This allows the data-collection intervals from any given
rcuscale guest OSes to line up with active periods in the other rcuscale
guest OSes, and also allows the thermal warm-up period required to obtain
consistent results from one test to the next.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
The current affinity check works fine until there are more reader
processes than CPUs, at which point the affinity check is looking for
non-existent CPUs. This commit therefore applies the same modulus to
the check as is present in the set_cpus_allowed_ptr() call.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Currently, running rcutorture test with torture_type=rcu fwd_progress=8
n_barrier_cbs=8 nocbs_nthreads=8 nocbs_toggle=100 onoff_interval=60
test_boost=2, will trigger the following warning:
WARNING: CPU: 19 PID: 100 at kernel/rcu/tree_nocb.h:1061 rcu_nocb_rdp_deoffload+0x292/0x2a0
RIP: 0010:rcu_nocb_rdp_deoffload+0x292/0x2a0
Call Trace:
<TASK>
? __warn+0x7e/0x120
? rcu_nocb_rdp_deoffload+0x292/0x2a0
? report_bug+0x18e/0x1a0
? handle_bug+0x3d/0x70
? exc_invalid_op+0x18/0x70
? asm_exc_invalid_op+0x1a/0x20
? rcu_nocb_rdp_deoffload+0x292/0x2a0
rcu_nocb_cpu_deoffload+0x70/0xa0
rcu_nocb_toggle+0x136/0x1c0
? __pfx_rcu_nocb_toggle+0x10/0x10
kthread+0xd1/0x100
? __pfx_kthread+0x10/0x10
ret_from_fork+0x2f/0x50
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
CPU0 CPU2 CPU3
//rcu_nocb_toggle //nocb_cb_wait //rcutorture
// deoffload CPU1 // process CPU1's rdp
rcu_barrier()
rcu_segcblist_entrain()
rcu_segcblist_add_len(1);
// len == 2
// enqueue barrier
// callback to CPU1's
// rdp->cblist
rcu_do_batch()
// invoke CPU1's rdp->cblist
// callback
rcu_barrier_callback()
rcu_barrier()
mutex_lock(&rcu_state.barrier_mutex);
// still see len == 2
// enqueue barrier callback
// to CPU1's rdp->cblist
rcu_segcblist_entrain()
rcu_segcblist_add_len(1);
// len == 3
// decrement len
rcu_segcblist_add_len(-2);
kthread_parkme()
// CPU1's rdp->cblist len == 1
// Warn because there is
// still a pending barrier
// trigger warning
WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist));
cpus_read_unlock();
// wait CPU1 to comes online and
// invoke barrier callback on
// CPU1 rdp's->cblist
wait_for_completion(&rcu_state.barrier_completion);
// deoffload CPU4
cpus_read_lock()
rcu_barrier()
mutex_lock(&rcu_state.barrier_mutex);
// block on barrier_mutex
// wait rcu_barrier() on
// CPU3 to unlock barrier_mutex
// but CPU3 unlock barrier_mutex
// need to wait CPU1 comes online
// when CPU1 going online will block on cpus_write_lock
The above scenario will not only trigger a WARN_ON_ONCE(), but also
trigger a deadlock.
Thanks to nocb locking, a second racing rcu_barrier() on an offline CPU
will either observe the decremented callback counter down to 0 and spare
the callback enqueue, or rcuo will observe the new callback and keep
rdp->nocb_cb_sleep to false.
Therefore check rdp->nocb_cb_sleep before parking to make sure no
further rcu_barrier() is waiting on the rdp.
Fixes: 1fcb932c8b ("rcu/nocb: Simplify (de-)offloading state machine")
Suggested-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
KCSAN reports a data race when access the krcp->monitor_work.timer.expires
variable in the schedule_delayed_monitor_work() function:
<snip>
BUG: KCSAN: data-race in __mod_timer / kvfree_call_rcu
read to 0xffff888237d1cce8 of 8 bytes by task 10149 on cpu 1:
schedule_delayed_monitor_work kernel/rcu/tree.c:3520 [inline]
kvfree_call_rcu+0x3b8/0x510 kernel/rcu/tree.c:3839
trie_update_elem+0x47c/0x620 kernel/bpf/lpm_trie.c:441
bpf_map_update_value+0x324/0x350 kernel/bpf/syscall.c:203
generic_map_update_batch+0x401/0x520 kernel/bpf/syscall.c:1849
bpf_map_do_batch+0x28c/0x3f0 kernel/bpf/syscall.c:5143
__sys_bpf+0x2e5/0x7a0
__do_sys_bpf kernel/bpf/syscall.c:5741 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5739 [inline]
__x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5739
x64_sys_call+0x2625/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:322
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
write to 0xffff888237d1cce8 of 8 bytes by task 56 on cpu 0:
__mod_timer+0x578/0x7f0 kernel/time/timer.c:1173
add_timer_global+0x51/0x70 kernel/time/timer.c:1330
__queue_delayed_work+0x127/0x1a0 kernel/workqueue.c:2523
queue_delayed_work_on+0xdf/0x190 kernel/workqueue.c:2552
queue_delayed_work include/linux/workqueue.h:677 [inline]
schedule_delayed_monitor_work kernel/rcu/tree.c:3525 [inline]
kfree_rcu_monitor+0x5e8/0x660 kernel/rcu/tree.c:3643
process_one_work kernel/workqueue.c:3229 [inline]
process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3310
worker_thread+0x51d/0x6f0 kernel/workqueue.c:3391
kthread+0x1d1/0x210 kernel/kthread.c:389
ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 56 Comm: kworker/u8:4 Not tainted 6.12.0-rc2-syzkaller-00050-g5b7c893ed5ed #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Workqueue: events_unbound kfree_rcu_monitor
<snip>
kfree_rcu_monitor() rearms the work if a "krcp" has to be still
offloaded and this is done without holding krcp->lock, whereas
the kvfree_call_rcu() holds it.
Fix it by acquiring the "krcp->lock" for kfree_rcu_monitor() so
both functions do not race anymore.
Reported-by: syzbot+061d370693bdd99f9d34@syzkaller.appspotmail.com
Link: https://lore.kernel.org/lkml/ZxZ68KmHDQYU0yfD@pc636/T/
Fixes: 8fc5494ad5 ("rcu/kvfree: Move need_offload_krc() out of krcp->lock")
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Code after the return statement is dead. Enable preemption before
returning from srcu_drive_gp().
This will be important when/if PREEMPT_AUTO (lazy resched) gets merged.
Fixes: 65b4a59557 ("srcu: Make Tiny SRCU explicitly disable preemption")
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit removes the open-coded one-byte cmpxchg() emulation from
rcu_trc_cmpxchg_need_qs(), replacing it with just cmpxchg() given the
latter's new-found ability to handle single-byte arguments across all
architectures.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit tests the ->start_poll() and ->start_poll_full() functions
with interrupts disabled, but only for RCU variants setting the
->start_poll_irqsoff flag.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
The header comment for both start_poll_synchronize_rcu() and
start_poll_synchronize_rcu_full() state that interrupts must be enabled
when calling these two functions, and there is a lockdep assertion in
start_poll_synchronize_rcu_common() enforcing this restriction. However,
there is no need for this restrictions, as can be seen in call_rcu(),
which does wakeups when interrupts are disabled.
This commit therefore removes the lockdep assertion and the comments.
Reported-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
There are now architectures for which all deep-idle and entry-exit
functions are properly inlined or marked noinstr. Such architectures do
not need synchronize_rcu_tasks_rude(), or will not once RCU Tasks has
been modified to pay attention to idle tasks. This commit therefore
allows a CONFIG_ARCH_HAS_NOINSTR_MARKINGS Kconfig option to turn
synchronize_rcu_tasks_rude() into a no-op.
To facilitate testing, kernels built by rcutorture scripting will enable
RCU Tasks Trace even on systems that do not need it.
[ paulmck: Apply Peter Zijlstra feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
The RCU_NOCB_CPU help text currently fails to mention rcuog kthreads,
so this commit adds this information.
Reported-by: Olivier Langlois <olivier@trillion01.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
sizeof(unsigned long) * 8 is the number of bits in an unsigned long
variable, replace it with BITS_PER_LONG macro to make it simpler.
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This silences the following coccinelle warning:
WARNING: sum of probable bitmasks, consider |
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Reviewed-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit creates a new srcu-lite option for the refscale.scale_type
module parameter that selects srcu_read_lock_lite() and
srcu_read_unlock_lite().
[ paulmck: Apply Dan Carpenter feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit causes bit 0x4 of rcutorture.reader_flavor to select the new
srcu_read_lock_lite() and srcu_read_unlock_lite() functions.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit adds an rcutorture.reader_flavor parameter whose bits
correspond to reader flavors. For example, SRCU's readers are 0x1 for
normal and 0x2 for NMI-safe.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit prepares for testing of multiple SRCU reader flavors by
expanding RCUTORTURE_RDR_MASK_1 and RCUTORTURE_RDR_MASK_2 from a single
bit to eight bits, allowing them to accommodate the return values from
multiple calls to srcu_read_lock*(). This will in turn permit better
testing coverage for these SRCU reader flavors, including testing of
the diagnostics for inproper use of mixed reader flavors.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit moves __srcu_read_lock_lite() and __srcu_read_unlock_lite()
into include/linux/srcu.h and marks them "static inline" so that they
can be inlined into srcu_read_lock_lite() and srcu_read_unlock_lite(),
respectively. They are not hand-inlined due to Tree SRCU and Tiny SRCU
having different implementations.
The earlier removal of smp_mb() combined with the inlining produce
significant single-percentage performance wins.
Link: https://lore.kernel.org/all/CAEf4BzYgiNmSb=ZKQ65tm6nJDi1UX2Gq26cdHSH1mPwXJYZj5g@mail.gmail.com/
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This patch adds srcu_read_lock_lite() and srcu_read_unlock_lite(), which
dispense with the read-side smp_mb() but also are restricted to code
regions that RCU is watching. If a given srcu_struct structure uses
srcu_read_lock_lite() and srcu_read_unlock_lite(), it is not permitted
to use any other SRCU read-side marker, before, during, or after.
Another price of light-weight readers is heavier weight grace periods.
Such readers mean that SRCU grace periods on srcu_struct structures
used by light-weight readers will incur at least two calls to
synchronize_rcu(). In addition, normal SRCU grace periods for
light-weight-reader srcu_struct structures never auto-expedite.
Note that expedited SRCU grace periods for light-weight-reader
srcu_struct structures still invoke synchronize_rcu(), not
synchronize_srcu_expedited(). Something about wishing to keep
the IPIs down to a dull roar.
The srcu_read_lock_lite() and srcu_read_unlock_lite() functions may not
(repeat, *not*) be used from NMI handlers, but if this is needed, an
additional flavor of SRCU reader can be added by some future commit.
[ paulmck: Apply Alexei Starovoitov expediting feedback. ]
[ paulmck: Apply kernel test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: kernel test robot <oliver.sang@intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit creates SRCU_READ_FLAVOR_NORMAL and SRCU_READ_FLAVOR_NMI
C-preprocessor macros for srcu_read_lock() and srcu_read_lock_nmisafe(),
respectively. These replace the old true/false values that were
previously passed to srcu_check_read_flavor(). In addition, the
srcu_check_read_flavor() function itself requires a bit of rework to
handle bitmasks instead of true/false values.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Currently, there are only two flavors of readers, normal and NMI-safe.
Very straightforward state updates suffice to check for erroneous
mixing of reader flavors on a given srcu_struct structure. This commit
upgrades the checking in preparation for the addition of light-weight
(as in memory-barrier-free) readers.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Currently, there are only two flavors of readers, normal and NMI-safe.
A number of fields, functions, and types reflect this restriction.
This renaming-only commit prepares for the addition of light-weight
(as in memory-barrier-free) readers. OK, OK, there is also a drive-by
white-space fixeup!
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit pushes the grace-period-end checks further down into
rcu_dump_cpu_stacks(), and also uses lockless checks coupled with
finer-grained locking.
The result is that the current leaf rcu_node structure's ->lock is
acquired only if a stack backtrace might be needed from the current CPU,
and is held across only that CPU's backtrace. As a result, if there are
no stalled CPUs associated with a given rcu_node structure, then its
->lock will not be acquired at all. On large systems, it is usually
(though not always) the case that a small number of CPUs are stalling
the current grace period, which means that the ->lock need be acquired
only for a small fraction of the rcu_node structures.
[ paulmck: Apply Dan Carpenter feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Even though the open-coded expressions usually fit on one line, this
commit replaces them with a call to a new srcu_gp_is_expedited()
helper function in order to improve readability.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
SRCU auto-expedites grace periods that follow a sufficiently long idle
period, and the srcu_might_be_idle() function is used to make this
decision. However, the upcoming light-weight SRCU readers will not do
auto-expediting because doing so would cause the grace-period machinery
to invoke synchronize_rcu_expedited() twice, with IPIs all around.
However, software-engineering considerations force this determination
to remain in srcu_might_be_idle().
This commit therefore changes the name of srcu_might_be_idle() to
srcu_should_expedite(), thus moving from what it currently does to why
it does it, this latter being more future-proof.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
The value of ARRAY_SIZE() can be determined at compile time, so if both
sides of the equation are ARRAY_SIZE(), using BUILD_BUG_ON() can help us
catch the problem earlier.
While there are cases where unequal array sizes will work, there is no
point in allowing them, so it makes more sense to force them to be equal
using BUILD_BUG_ON().
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Currently, once an RCU CPU stall warning decides to dump the stalling
CPUs' stacks, the rcu_dump_cpu_stacks() function persists until it
has gone through the full list. Unfortunately, if the stalled grace
periods ends midway through, this function will be dumping stacks of
innocent-bystander CPUs that happen to be blocking not the old grace
period, but instead the new one. This can cause serious confusion.
This commit therefore stops dumping stacks if and when the stalled grace
period ends.
[ paulmck: Apply Joel Fernandes feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
The rcu_gp_might_be_stalled() function is no longer used, so this commit
removes it.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Conflicts:
kernel/sched/ext.c
There's a context conflict between this upstream commit:
3fdb9ebcec sched_ext: Start schedulers with consistent p->scx.slice values
... and this fix in sched/urgent:
98442f0ccd sched: Fix delayed_dequeue vs switched_from_fair()
Resolve it.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Sean noted that ever since commit 152e11f6df ("sched/fair: Implement
delayed dequeue") KVM's preemption notifiers have started
mis-classifying preemption vs blocking.
Notably p->on_rq is no longer sufficient to determine if a task is
runnable or blocked -- the aforementioned commit introduces tasks that
remain on the runqueue even through they will not run again, and
should be considered blocked for many cases.
Add the task_is_runnable() helper to classify things and audit all
external users of the p->on_rq state. Also add a few comments.
Fixes: 152e11f6df ("sched/fair: Implement delayed dequeue")
Reported-by: Sean Christopherson <seanjc@google.com>
Tested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20241010091843.GK33184@noisy.programming.kicks-ass.net
After a CPU has set itself offline and before it eventually calls
rcutree_report_cpu_dead(), there are still opportunities for callbacks
to be enqueued, for example from a softirq. When that happens on NOCB,
the rcuog wake-up is deferred through an IPI to an online CPU in order
not to call into the scheduler and risk arming the RT-bandwidth after
hrtimers have been migrated out and disabled.
But performing a synchronized IPI from a softirq is buggy as reported in
the following scenario:
WARNING: CPU: 1 PID: 26 at kernel/smp.c:633 smp_call_function_single
Modules linked in: rcutorture torture
CPU: 1 UID: 0 PID: 26 Comm: migration/1 Not tainted 6.11.0-rc1-00012-g9139f93209d1 #1
Stopper: multi_cpu_stop+0x0/0x320 <- __stop_cpus+0xd0/0x120
RIP: 0010:smp_call_function_single
<IRQ>
swake_up_one_online
__call_rcu_nocb_wake
__call_rcu_common
? rcu_torture_one_read
call_timer_fn
__run_timers
run_timer_softirq
handle_softirqs
irq_exit_rcu
? tick_handle_periodic
sysvec_apic_timer_interrupt
</IRQ>
Fix this with forcing deferred rcuog wake up through the NOCB timer when
the CPU is offline. The actual wake up will happen from
rcutree_report_cpu_dead().
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202409231644.4c55582d-lkp@intel.com
Fixes: 9139f93209 ("rcu/nocb: Fix RT throttling hrtimer armed from offline CPU")
Reviewed-by: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Improve readability of kvfree_rcu_queue_batch() function
in away that, after a first batch queuing, the loop is break
and success value is returned to a caller.
There is no reason to loop and check batches further as all
outstanding objects have already been picked and attached to
a certain batch to complete an offloading.
Fixes: 2b55d6a42d ("rcu/kvfree: Add kvfree_rcu_barrier() API")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Closes: https://lore.kernel.org/lkml/ZvWUt2oyXRsvJRNc@pc636/T/
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
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Merge tag 'slab-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab
Pull slab updates from Vlastimil Babka:
"This time it's mostly refactoring and improving APIs for slab users in
the kernel, along with some debugging improvements.
- kmem_cache_create() refactoring (Christian Brauner)
Over the years have been growing new parameters to
kmem_cache_create() where most of them are needed only for a small
number of caches - most recently the rcu_freeptr_offset parameter.
To avoid adding new parameters to kmem_cache_create() and adjusting
all its callers, or creating new wrappers such as
kmem_cache_create_rcu(), we can now pass extra parameters using the
new struct kmem_cache_args. Not explicitly initialized fields
default to values interpreted as unused.
kmem_cache_create() is for now a wrapper that works both with the
new form: kmem_cache_create(name, object_size, args, flags) and the
legacy form: kmem_cache_create(name, object_size, align, flags,
ctor)
- kmem_cache_destroy() waits for kfree_rcu()'s in flight (Vlastimil
Babka, Uladislau Rezki)
Since SLOB removal, kfree() is allowed for freeing objects
allocated by kmem_cache_create(). By extension kfree_rcu() as
allowed as well, which can allow converting simple call_rcu()
callbacks that only do kmem_cache_free(), as there was never a
kmem_cache_free_rcu() variant. However, for caches that can be
destroyed e.g. on module removal, the cache owners knew to issue
rcu_barrier() first to wait for the pending call_rcu()'s, and this
is not sufficient for pending kfree_rcu()'s due to its internal
batching optimizations. Ulad has provided a new
kvfree_rcu_barrier() and to make the usage less error-prone,
kmem_cache_destroy() calls it. Additionally, destroying
SLAB_TYPESAFE_BY_RCU caches now again issues rcu_barrier()
synchronously instead of using an async work, because the past
motivation for async work no longer applies. Users of custom
call_rcu() callbacks should however keep calling rcu_barrier()
before cache destruction.
- Debugging use-after-free in SLAB_TYPESAFE_BY_RCU caches (Jann Horn)
Currently, KASAN cannot catch UAFs in such caches as it is legal to
access them within a grace period, and we only track the grace
period when trying to free the underlying slab page. The new
CONFIG_SLUB_RCU_DEBUG option changes the freeing of individual
object to be RCU-delayed, after which KASAN can poison them.
- Delayed memcg charging (Shakeel Butt)
In some cases, the memcg is uknown at allocation time, such as
receiving network packets in softirq context. With
kmem_cache_charge() these may be now charged later when the user
and its memcg is known.
- Misc fixes and improvements (Pedro Falcato, Axel Rasmussen,
Christoph Lameter, Yan Zhen, Peng Fan, Xavier)"
* tag 'slab-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab: (34 commits)
mm, slab: restore kerneldoc for kmem_cache_create()
io_uring: port to struct kmem_cache_args
slab: make __kmem_cache_create() static inline
slab: make kmem_cache_create_usercopy() static inline
slab: remove kmem_cache_create_rcu()
file: port to struct kmem_cache_args
slab: create kmem_cache_create() compatibility layer
slab: port KMEM_CACHE_USERCOPY() to struct kmem_cache_args
slab: port KMEM_CACHE() to struct kmem_cache_args
slab: remove rcu_freeptr_offset from struct kmem_cache
slab: pass struct kmem_cache_args to do_kmem_cache_create()
slab: pull kmem_cache_open() into do_kmem_cache_create()
slab: pass struct kmem_cache_args to create_cache()
slab: port kmem_cache_create_usercopy() to struct kmem_cache_args
slab: port kmem_cache_create_rcu() to struct kmem_cache_args
slab: port kmem_cache_create() to struct kmem_cache_args
slab: add struct kmem_cache_args
slab: s/__kmem_cache_create/do_kmem_cache_create/g
memcg: add charging of already allocated slab objects
mm/slab: Optimize the code logic in find_mergeable()
...
This pull request contains the following branches:
context_tracking.15.08.24a: Rename context tracking state related
symbols and remove references to "dynticks" in various context
tracking state variables and related helpers; force
context_tracking_enabled_this_cpu() to be inlined to avoid
leaving a noinstr section.
csd.lock.15.08.24a: Enhance CSD-lock diagnostic reports; add an API
to provide an indication of ongoing CSD-lock stall.
nocb.09.09.24a: Update and simplify RCU nocb code to handle
(de-)offloading of callbacks only for offline CPUs; fix RT
throttling hrtimer being armed from offline CPU.
rcutorture.14.08.24a: Remove redundant rcu_torture_ops get_gp_completed
fields; add SRCU ->same_gp_state and ->get_comp_state
functions; add generic test for NUM_ACTIVE_*RCU_POLL* for
testing RCU and SRCU polled grace periods; add CFcommon.arch
for arch-specific Kconfig options; print number of update types
in rcu_torture_write_types();
add rcutree.nohz_full_patience_delay testing to the TREE07
scenario; add a stall_cpu_repeat module parameter to test
repeated CPU stalls; add argument to limit number of CPUs a
guest OS can use in torture.sh;
rcustall.09.09.24a: Abbreviate RCU CPU stall warnings during CSD-lock
stalls; Allow dump_cpu_task() to be called without disabling
preemption; defer printing stall-warning backtrace when holding
rcu_node lock.
srcu.12.08.24a: Make SRCU gp seq wrap-around faster; add KCSAN checks
for concurrent updates to ->srcu_n_exp_nodelay and
->reschedule_count which are used in heuristics governing
auto-expediting of normal SRCU grace periods and
grace-period-state-machine delays; mark idle SRCU-barrier
callbacks to help identify stuck SRCU-barrier callback.
rcu.tasks.14.08.24a: Remove RCU Tasks Rude asynchronous APIs as they
are no longer used; stop testing RCU Tasks Rude asynchronous
APIs; fix access to non-existent percpu regions; check
processor-ID assumptions during chosen CPU calculation for
callback enqueuing; update description of rtp->tasks_gp_seq
grace-period sequence number; add rcu_barrier_cb_is_done()
to identify whether a given rcu_barrier callback is stuck;
mark idle Tasks-RCU-barrier callbacks; add
*torture_stats_print() functions to print detailed
diagnostics for Tasks-RCU variants; capture start time of
rcu_barrier_tasks*() operation to help distinguish a hung
barrier operation from a long series of barrier operations.
rcu_scaling_tests.15.08.24a:
refscale: Add a TINY scenario to support tests of Tiny RCU
and Tiny SRCU; Optimize process_durations() operation;
rcuscale: Dump stacks of stalled rcu_scale_writer() instances;
dump grace-period statistics when rcu_scale_writer() stalls;
mark idle RCU-barrier callbacks to identify stuck RCU-barrier
callbacks; print detailed grace-period and barrier diagnostics
on rcu_scale_writer() hangs for Tasks-RCU variants; warn if
async module parameter is specified for RCU implementations
that do not have async primitives such as RCU Tasks Rude;
make all writer tasks report upon hang; tolerate repeated
GFP_KERNEL failure in rcu_scale_writer(); use special allocator
for rcu_scale_writer(); NULL out top-level pointers to heap
memory to avoid double-free bugs on modprobe failures; maintain
per-task instead of per-CPU callbacks count to avoid any issues
with migration of either tasks or callbacks; constify struct
ref_scale_ops.
fixes.12.08.24a: Use system_unbound_wq for kfree_rcu work to avoid
disturbing isolated CPUs.
misc.11.08.24a: Warn on unexpected rcu_state.srs_done_tail state;
Better define "atomic" for list_replace_rcu() and
hlist_replace_rcu() routines; annotate struct
kvfree_rcu_bulk_data with __counted_by().
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Merge tag 'rcu.release.v6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux
Pull RCU updates from Neeraj Upadhyay:
"Context tracking:
- rename context tracking state related symbols and remove references
to "dynticks" in various context tracking state variables and
related helpers
- force context_tracking_enabled_this_cpu() to be inlined to avoid
leaving a noinstr section
CSD lock:
- enhance CSD-lock diagnostic reports
- add an API to provide an indication of ongoing CSD-lock stall
nocb:
- update and simplify RCU nocb code to handle (de-)offloading of
callbacks only for offline CPUs
- fix RT throttling hrtimer being armed from offline CPU
rcutorture:
- remove redundant rcu_torture_ops get_gp_completed fields
- add SRCU ->same_gp_state and ->get_comp_state functions
- add generic test for NUM_ACTIVE_*RCU_POLL* for testing RCU and SRCU
polled grace periods
- add CFcommon.arch for arch-specific Kconfig options
- print number of update types in rcu_torture_write_types()
- add rcutree.nohz_full_patience_delay testing to the TREE07 scenario
- add a stall_cpu_repeat module parameter to test repeated CPU stalls
- add argument to limit number of CPUs a guest OS can use in
torture.sh
rcustall:
- abbreviate RCU CPU stall warnings during CSD-lock stalls
- Allow dump_cpu_task() to be called without disabling preemption
- defer printing stall-warning backtrace when holding rcu_node lock
srcu:
- make SRCU gp seq wrap-around faster
- add KCSAN checks for concurrent updates to ->srcu_n_exp_nodelay and
->reschedule_count which are used in heuristics governing
auto-expediting of normal SRCU grace periods and
grace-period-state-machine delays
- mark idle SRCU-barrier callbacks to help identify stuck
SRCU-barrier callback
rcu tasks:
- remove RCU Tasks Rude asynchronous APIs as they are no longer used
- stop testing RCU Tasks Rude asynchronous APIs
- fix access to non-existent percpu regions
- check processor-ID assumptions during chosen CPU calculation for
callback enqueuing
- update description of rtp->tasks_gp_seq grace-period sequence
number
- add rcu_barrier_cb_is_done() to identify whether a given
rcu_barrier callback is stuck
- mark idle Tasks-RCU-barrier callbacks
- add *torture_stats_print() functions to print detailed diagnostics
for Tasks-RCU variants
- capture start time of rcu_barrier_tasks*() operation to help
distinguish a hung barrier operation from a long series of barrier
operations
refscale:
- add a TINY scenario to support tests of Tiny RCU and Tiny
SRCU
- optimize process_durations() operation
rcuscale:
- dump stacks of stalled rcu_scale_writer() instances and
grace-period statistics when rcu_scale_writer() stalls
- mark idle RCU-barrier callbacks to identify stuck RCU-barrier
callbacks
- print detailed grace-period and barrier diagnostics on
rcu_scale_writer() hangs for Tasks-RCU variants
- warn if async module parameter is specified for RCU implementations
that do not have async primitives such as RCU Tasks Rude
- make all writer tasks report upon hang
- tolerate repeated GFP_KERNEL failure in rcu_scale_writer()
- use special allocator for rcu_scale_writer()
- NULL out top-level pointers to heap memory to avoid double-free
bugs on modprobe failures
- maintain per-task instead of per-CPU callbacks count to avoid any
issues with migration of either tasks or callbacks
- constify struct ref_scale_ops
Fixes:
- use system_unbound_wq for kfree_rcu work to avoid disturbing
isolated CPUs
Misc:
- warn on unexpected rcu_state.srs_done_tail state
- better define "atomic" for list_replace_rcu() and
hlist_replace_rcu() routines
- annotate struct kvfree_rcu_bulk_data with __counted_by()"
* tag 'rcu.release.v6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (90 commits)
rcu: Defer printing stall-warning backtrace when holding rcu_node lock
rcu/nocb: Remove superfluous memory barrier after bypass enqueue
rcu/nocb: Conditionally wake up rcuo if not already waiting on GP
rcu/nocb: Fix RT throttling hrtimer armed from offline CPU
rcu/nocb: Simplify (de-)offloading state machine
context_tracking: Tag context_tracking_enabled_this_cpu() __always_inline
context_tracking, rcu: Rename rcu_dyntick trace event into rcu_watching
rcu: Update stray documentation references to rcu_dynticks_eqs_{enter, exit}()
rcu: Rename rcu_momentary_dyntick_idle() into rcu_momentary_eqs()
rcu: Rename rcu_implicit_dynticks_qs() into rcu_watching_snap_recheck()
rcu: Rename dyntick_save_progress_counter() into rcu_watching_snap_save()
rcu: Rename struct rcu_data .exp_dynticks_snap into .exp_watching_snap
rcu: Rename struct rcu_data .dynticks_snap into .watching_snap
rcu: Rename rcu_dynticks_zero_in_eqs() into rcu_watching_zero_in_eqs()
rcu: Rename rcu_dynticks_in_eqs_since() into rcu_watching_snap_stopped_since()
rcu: Rename rcu_dynticks_in_eqs() into rcu_watching_snap_in_eqs()
rcu: Rename rcu_dynticks_eqs_online() into rcu_watching_online()
context_tracking, rcu: Rename rcu_dynticks_curr_cpu_in_eqs() into rcu_is_watching_curr_cpu()
context_tracking, rcu: Rename rcu_dynticks_task*() into rcu_task*()
refscale: Constify struct ref_scale_ops
...
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Merge tag 'printk-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux
Pull printk updates from Petr Mladek:
"This is the "last" part of the support for the new nbcon consoles.
Where "nbcon" stays for "No Big console lock CONsoles" aka not under
the console_lock.
New callbacks are added to struct console:
- write_thread() for flushing nbcon consoles in task context.
- write_atomic() for flushing nbcon consoles in atomic context,
including NMI.
- con->device_lock() and device_unlock() for taking the driver
specific lock, for example, port->lock.
New printk-specific kthreads are created:
- per-console kthreads which get responsible for flushing normal
priority messages on nbcon consoles.
- thread which gets responsible for flushing normal priority messages
on all consoles when CONFIG_RT enabled.
The new callbacks are called under a special per-console lock which
has already been added back in v6.7. It allows to distinguish three
severities: normal, emergency, and panic. A context with a higher
priority could take over the ownership when it is safe even in the
middle of handling a record. The panic context could do it even when
it is not safe. But it is allowed only for the final desperate flush
before entering the infinite loop.
The new lock helps to flush the messages directly in emergency and
panic contexts. But it is not enough in all situations:
- console_lock() is still need for synchronization against boot
consoles.
- con->device_lock() is need for synchronization against other
operations on the same HW, e.g. serial port speed setting,
non-printk related read/write.
The dependency on con->device_lock() is mutual. Any code taking the
driver specific lock has to acquire the related nbcon console context
as well. For example, see the new uart_port_lock() API. It provides
the necessary synchronization against emergency and panic contexts
where the messages are flushed only under the new per-console lock.
Maybe surprisingly, a quite tricky part is the decision how to flush
the consoles in various situations. It has to take into account:
- message priority: normal, emergency, panic
- scheduling context: task, atomic, deferred_legacy
- registered consoles: boot, legacy, nbcon
- threads are running: early boot, suspend, shutdown, panic
- caller: printk(), pr_flush(), printk_flush_in_panic(),
console_unlock(), console_start(), ...
The primary decision is made in printk_get_console_flush_type(). It
creates a hint what the caller should do:
- flush nbcon consoles directly or via the kthread
- call the legacy loop (console_unlock()) directly or via irq_work
The existing behavior is preserved for the legacy consoles. The only
exception is that they are not longer flushed directly from printk()
in panic() before CPUs are stopped. But this blocking happens only
when at least one nbcon console is registered. The motivation is to
increase a chance to produce the crash dump. They legacy consoles
might create a deadlock in compare with nbcon consoles. The nbcon
console should allow to see the messages even when the crash dump
fails.
There are three possible ways how nbcon consoles are flushed:
- The per-nbcon-console kthread is responsible for flushing messages
added with the normal priority. This is the default mode.
- The legacy loop, aka console_unlock(), is used when there is still
a boot console registered. There is no easy way how to match an
early console driver with a nbcon console driver. And the
console_lock() provides the only reliable serialization at the
moment.
The legacy loop uses either con->write_atomic() or
con->write_thread() callbacks depending on whether it is allowed to
schedule. The atomic variant has to be used from printk().
- In other situations, the messages are flushed directly using
write_atomic() which can be called in any context, including NMI.
It is primary needed during early boot or shutdown, in emergency
situations, and panic.
The emergency priority is used by a code called within
nbcon_cpu_emergency_enter()/exit(). At the moment, it is used in four
situations: WARN(), Oops, lockdep, and RCU stall reports.
Finally, there is no nbcon console at the moment. It means that the
changes should _not_ modify the existing behavior. The only exception
is CONFIG_RT which would force offloading the legacy loop, for normal
priority context, into the dedicated kthread"
* tag 'printk-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: (54 commits)
printk: Avoid false positive lockdep report for legacy printing
printk: nbcon: Assign nice -20 for printing threads
printk: Implement legacy printer kthread for PREEMPT_RT
tty: sysfs: Add nbcon support for 'active'
proc: Add nbcon support for /proc/consoles
proc: consoles: Add notation to c_start/c_stop
printk: nbcon: Show replay message on takeover
printk: Provide helper for message prepending
printk: nbcon: Rely on kthreads for normal operation
printk: nbcon: Use thread callback if in task context for legacy
printk: nbcon: Relocate nbcon_atomic_emit_one()
printk: nbcon: Introduce printer kthreads
printk: nbcon: Init @nbcon_seq to highest possible
printk: nbcon: Add context to usable() and emit()
printk: Flush console on unregister_console()
printk: Fail pr_flush() if before SYSTEM_SCHEDULING
printk: nbcon: Add function for printers to reacquire ownership
printk: nbcon: Use raw_cpu_ptr() instead of open coding
printk: Use the BITS_PER_LONG macro
lockdep: Mark emergency sections in lockdep splats
...
The rcu_dump_cpu_stacks() holds the leaf rcu_node structure's ->lock
when dumping the stakcks of any CPUs stalling the current grace period.
This lock is held to prevent confusion that would otherwise occur when
the stalled CPU reported its quiescent state (and then went on to do
unrelated things) just as the backtrace NMI was heading towards it.
This has worked well, but on larger systems has recently been observed
to cause severe lock contention resulting in CSD-lock stalls and other
general unhappiness.
This commit therefore does printk_deferred_enter() before acquiring
the lock and printk_deferred_exit() after releasing it, thus deferring
the overhead of actually outputting the stack trace out of that lock's
critical section.
Reported-by: Rik van Riel <riel@surriel.com>
Suggested-by: Rik van Riel <riel@surriel.com>
Signed-off-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Pre-GP accesses performed by the update side must be ordered against
post-GP accesses performed by the readers. This is ensured by the
bypass or nocb locking on enqueue time, followed by the fully ordered
rnp locking initiated while callbacks are accelerated, and then
propagated throughout the whole GP lifecyle associated with the
callbacks.
Therefore the explicit barrier advertizing ordering between bypass
enqueue and rcuo wakeup is superfluous. If anything, it would even only
order the first bypass callback enqueue against the rcuo wakeup and
ignore all the subsequent ones.
Remove the needless barrier.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
A callback enqueuer currently wakes up the rcuo kthread if it is adding
the first non-done callback of a CPU, whether the kthread is waiting on
a grace period or not (unless the CPU is offline).
This looks like a desired behaviour because then the rcuo kthread
doesn't wait for the end of the current grace period to handle the
callback. It is accelerated right away and assigned to the next grace
period. The GP kthread is notified about that fact and iterates with
the upcoming GP without sleeping in-between.
However this best-case scenario is contradicted by a few details,
depending on the situation:
1) If the callback is a non-bypass one queued with IRQs enabled, the
wake up only occurs if no other pending callbacks are on the list.
Therefore the theoretical "optimization" actually applies on rare
occasions.
2) If the callback is a non-bypass one queued with IRQs disabled, the
situation is similar with even more uncertainty due to the deferred
wake up.
3) If the callback is lazy, a few jiffies don't make any difference.
4) If the callback is bypass, the wake up timer is programmed 2 jiffies
ahead by rcuo in case the regular pending queue has been handled
in the meantime. The rare storm of callbacks can otherwise wait for
the currently elapsing grace period to be flushed and handled.
For all those reasons, the optimization is only theoretical and
occasional. Therefore it is reasonable that callbacks enqueuers only
wake up the rcuo kthread when it is not already waiting on a grace
period to complete.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
After a CPU is marked offline and until it reaches its final trip to
idle, rcuo has several opportunities to be woken up, either because
a callback has been queued in the meantime or because
rcutree_report_cpu_dead() has issued the final deferred NOCB wake up.
If RCU-boosting is enabled, RCU kthreads are set to SCHED_FIFO policy.
And if RT-bandwidth is enabled, the related hrtimer might be armed.
However this then happens after hrtimers have been migrated at the
CPUHP_AP_HRTIMERS_DYING stage, which is broken as reported by the
following warning:
Call trace:
enqueue_hrtimer+0x7c/0xf8
hrtimer_start_range_ns+0x2b8/0x300
enqueue_task_rt+0x298/0x3f0
enqueue_task+0x94/0x188
ttwu_do_activate+0xb4/0x27c
try_to_wake_up+0x2d8/0x79c
wake_up_process+0x18/0x28
__wake_nocb_gp+0x80/0x1a0
do_nocb_deferred_wakeup_common+0x3c/0xcc
rcu_report_dead+0x68/0x1ac
cpuhp_report_idle_dead+0x48/0x9c
do_idle+0x288/0x294
cpu_startup_entry+0x34/0x3c
secondary_start_kernel+0x138/0x158
Fix this with waking up rcuo using an IPI if necessary. Since the
existing API to deal with this situation only handles swait queue, rcuo
is only woken up from offline CPUs if it's not already waiting on a
grace period. In the worst case some callbacks will just wait for a
grace period to complete before being assigned to a subsequent one.
Reported-by: "Cheng-Jui Wang (王正睿)" <Cheng-Jui.Wang@mediatek.com>
Fixes: 5c0930ccaa ("hrtimers: Push pending hrtimers away from outgoing CPU earlier")
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Now that the (de-)offloading process can only apply to offline CPUs,
there is no more concurrency between rcu_core and nocb kthreads. Also
the mutation now happens on empty queues.
Therefore the state machine can be reduced to a single bit called
SEGCBLIST_OFFLOADED. Simplify the transition as follows:
* Upon offloading: queue the rdp to be added to the rcuog list and
wait for the rcuog kthread to set the SEGCBLIST_OFFLOADED bit. Unpark
rcuo kthread.
* Upon de-offloading: Park rcuo kthread. Queue the rdp to be removed
from the rcuog list and wait for the rcuog kthread to clear the
SEGCBLIST_OFFLOADED bit.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Add a kvfree_rcu_barrier() function. It waits until all
in-flight pointers are freed over RCU machinery. It does
not wait any GP completion and it is within its right to
return immediately if there are no outstanding pointers.
This function is useful when there is a need to guarantee
that a memory is fully freed before destroying memory caches.
For example, during unloading a kernel module.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
