linux.git/Documentation/locking, branch v6.12.80 Clone of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git kcsan, seqlock: Support seqcount_latch_t 2024-12-05T13:01:22+00:00 Marco Elver elver@google.com 2024-11-04T15:43:07+00:00 a694fc092838beaf7bed73477d273e180da34bc5 [ Upstream commit 5c1806c41ce0a0110db5dd4c483cf2dc28b3ddf0 ] 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: 88ecd153be95 ("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 Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 5c1806c41ce0a0110db5dd4c483cf2dc28b3ddf0 ]

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: 88ecd153be95 ("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
Signed-off-by: Sasha Levin <sashal@kernel.org>
hwspinlock: Introduce hwspin_lock_bust() 2024-05-29T19:52:26+00:00 Richard Maina quic_rmaina@quicinc.com 2024-05-29T18:09:55+00:00 7c327d56597d8de1680cf24e956b704270d3d84a 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> 
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>
locking/mutex: Clarify that mutex_unlock(), and most other sleeping locks, can still use the lock object after it's unlocked 2024-01-08T08:55:31+00:00 Ingo Molnar mingo@kernel.org 2024-01-08T08:31:16+00:00 2b9d9e0a9ba0e24cb9c78336481f0ed8b2bc1ff2 Clarify the mutex lock lifetime rules a bit more. Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Jann Horn <jannh@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/r/20231201121808.GL3818@noisy.programming.kicks-ass.net 
Clarify the mutex lock lifetime rules a bit more.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jann Horn <jannh@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231201121808.GL3818@noisy.programming.kicks-ass.net
locking/mutex: Document that mutex_unlock() is non-atomic 2023-12-01T10:27:43+00:00 Jann Horn jannh@google.com 2023-11-30T20:48:17+00:00 a51749ab34d9e5dec548fe38ede7e01e8bb26454 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 
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
Documentation: Fix typos 2023-08-18T17:29:03+00:00 Bjorn Helgaas bhelgaas@google.com 2023-08-14T21:28:22+00:00 d56b699d76d1b352f7a3d3a0a3e91c79b8612d94 Fix typos in Documentation. Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Link: https://lore.kernel.org/r/20230814212822.193684-4-helgaas@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net> 
Fix typos in Documentation.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20230814212822.193684-4-helgaas@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Documentation: use capitalization for chapters and acronyms 2023-05-16T18:49:31+00:00 Randy Dunlap rdunlap@infradead.org 2023-05-16T00:15:18+00:00 96e3cc270d61cb9945b1c2894effcba15010f097 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> 
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>
docs: locking: refer to the actual existing config names 2023-02-23T19:26:00+00:00 Lukas Bulwahn lukas.bulwahn@gmail.com 2023-02-20T16:57:49+00:00 01178ee713100c7d7e738992134545acff472d1d 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> 
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>
Remove duplicate words inside documentation 2022-09-27T19:21:43+00:00 Akhil Raj lf32.dev@gmail.com 2022-08-27T14:53:59+00:00 d2bef8e1037cc69695c6b146bb05ce053450e0de I have removed repeated `the` inside the documentation Signed-off-by: Akhil Raj <lf32.dev@gmail.com> Link: https://lore.kernel.org/r/20220827145359.32599-1-lf32.dev@gmail.com Signed-off-by: Jonathan Corbet <corbet@lwn.net> 
I have removed repeated `the` inside the documentation

Signed-off-by: Akhil Raj <lf32.dev@gmail.com>
Link: https://lore.kernel.org/r/20220827145359.32599-1-lf32.dev@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Documentation: Fix duplicate statement about raw_spinlock_t type 2022-03-25T19:30:08+00:00 Guilherme G. Piccoli gpiccoli@igalia.com 2022-03-21T14:41:33+00:00 8d6451b9a51b555be2c9a6c326a980b2de00741a 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: 919e9e6395cf ("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> 
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: 919e9e6395cf ("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>
Documentation/locking/locktypes: Fix PREEMPT_RT _bh() description 2022-03-04T17:13:19+00:00 Andrew Halaney ahalaney@redhat.com 2022-02-24T21:23:12+00:00 0d2be10b3037c12d68003856b8d6c83d1b80e0c9 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> 
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>