linux-stable.git/Documentation/locking, branch linux-5.15.y

kcsan, seqlock: Support seqcount_latch_t

2024-12-14T18:50:46+00:00

[ 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 
Co-developed-by: "Peter Zijlstra (Intel)" 
Signed-off-by: "Peter Zijlstra (Intel)" 
Signed-off-by: Marco Elver 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20241104161910.780003-4-elver@google.com
Signed-off-by: Sasha Levin

hwspinlock: Introduce hwspin_lock_bust()

2024-09-12T09:07:41+00:00

[ Upstream commit 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 
Reviewed-by: Bjorn Andersson 
Signed-off-by: Chris Lew 
Link: https://lore.kernel.org/r/20240529-hwspinlock-bust-v3-1-c8b924ffa5a2@quicinc.com
Signed-off-by: Bjorn Andersson 
Signed-off-by: Sasha Levin

Documentation/locking/locktypes: Update migrate_disable() bits.

2021-12-14T09:57:18+00:00

commit 6a631c0432dcccbcf45839016a07c015e335e9ae upstream.

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: 74d862b682f51 ("sched: Make migrate_disable/enable() independent of RT")
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Daniel Borkmann 
Link: https://lore.kernel.org/bpf/20211127163200.10466-2-bigeasy@linutronix.de
Signed-off-by: Greg Kroah-Hartman

Documentation: locking: fix references

2021-08-24T19:20:39+00:00

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 
Link: https://lore.kernel.org/r/20210823183143.1691344-1-aahringo@redhat.com
Signed-off-by: Jonathan Corbet

locking/lockdep,doc: Improve readability of the block matrix

2021-05-31T08:14:54+00:00

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 
Suggested-by: Boqun Feng 
Signed-off-by: Xiongwei Song 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Boqun Feng 
Link: https://lkml.kernel.org/r/1621868745-23311-1-git-send-email-sxwjean@me.com

Documentation: seqlock: s/LOCKTYPE/LOCKNAME/g

2020-12-09T16:08:49+00:00

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: 6dd699b13d53 ("seqlock: seqcount_LOCKNAME_t: Standardize naming convention")
Signed-off-by: Ahmed S. Darwish 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20201206162143.14387-2-a.darwish@linutronix.de

docs: lockdep-design: fix some warning issues

2020-10-28T17:41:15+00:00

There are several warnings caused by a recent change
224ec489d3cd ("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: 224ec489d3cd ("lockdep/Documention: Recursive read lock detection reasoning")
Signed-off-by: Mauro Carvalho Chehab
Link: https://lore.kernel.org/r/3b9431ac5c01e38111cd59928a93e7259ab7db0f.1603791716.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet

seqlock: Introduce seqcount_latch_t

2020-09-10T09:19:28+00:00

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: 9b0fd802e8c0 ("seqcount: Add raw_write_seqcount_latch()")
References: 7fc26327b756 ("seqlock: Introduce raw_read_seqcount_latch()")
References: aadd6e5caaac ("time/sched_clock: Use raw_read_seqcount_latch()")
Signed-off-by: Ahmed S. Darwish 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20200827114044.11173-4-a.darwish@linutronix.de

lockdep/Documention: Recursive read lock detection reasoning

2020-08-26T10:42:03+00:00

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 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20200807074238.1632519-3-boqun.feng@gmail.com

Documentation/locking/locktypes: Fix local_locks documentation

2020-08-26T10:42:02+00:00

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 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Will Deacon 
Link: https://lkml.kernel.org/r/CAApg2=SKxQ3Sqwj6TZnV-0x0cKLXFKDaPvXT4N15MPDMKq724g@mail.gmail.com