When a interruptible mutex locker is interrupted by a signal
without acquiring this lock and removed from the wait queue.
if the mutex isn't contended enough to have a waiter
put into the wait queue again, the setting of the WAITER
bit will force mutex locker to go into the slowpath to
acquire the lock every time, so if the wait queue is empty,
the WAITER bit need to be clear.
Fixes: 040a0a3710 ("mutex: Add support for wound/wait style locks")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210517034005.30828-1-qiang.zhang@windriver.com
Make the code more readable by replacing the atomic_cmpxchg_acquire()
by an equivalent atomic_try_cmpxchg_acquire() and change atomic_add()
to atomic_or().
For architectures that use qrwlock, I do not find one that has an
atomic_add() defined but not an atomic_or(). I guess it should be fine
by changing atomic_add() to atomic_or().
Note that the previous use of atomic_add() isn't wrong as only one
writer that is the wait_lock owner can set the waiting flag and the
flag will be cleared later on when acquiring the write lock.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20210426185017.19815-1-longman@redhat.com
Pull locking updates from Ingo Molnar:
- rtmutex cleanup & spring cleaning pass that removes ~400 lines of
code
- Futex simplifications & cleanups
- Add debugging to the CSD code, to help track down a tenacious race
(or hw problem)
- Add lockdep_assert_not_held(), to allow code to require a lock to not
be held, and propagate this into the ath10k driver
- Misc LKMM documentation updates
- Misc KCSAN updates: cleanups & documentation updates
- Misc fixes and cleanups
- Fix locktorture bugs with ww_mutexes
* tag 'locking-core-2021-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (44 commits)
kcsan: Fix printk format string
static_call: Relax static_call_update() function argument type
static_call: Fix unused variable warn w/o MODULE
locking/rtmutex: Clean up signal handling in __rt_mutex_slowlock()
locking/rtmutex: Restrict the trylock WARN_ON() to debug
locking/rtmutex: Fix misleading comment in rt_mutex_postunlock()
locking/rtmutex: Consolidate the fast/slowpath invocation
locking/rtmutex: Make text section and inlining consistent
locking/rtmutex: Move debug functions as inlines into common header
locking/rtmutex: Decrapify __rt_mutex_init()
locking/rtmutex: Remove pointless CONFIG_RT_MUTEXES=n stubs
locking/rtmutex: Inline chainwalk depth check
locking/rtmutex: Move rt_mutex_debug_task_free() to rtmutex.c
locking/rtmutex: Remove empty and unused debug stubs
locking/rtmutex: Consolidate rt_mutex_init()
locking/rtmutex: Remove output from deadlock detector
locking/rtmutex: Remove rtmutex deadlock tester leftovers
locking/rtmutex: Remove rt_mutex_timed_lock()
MAINTAINERS: Add myself as futex reviewer
locking/mutex: Remove repeated declaration
...
Pull lockdep capacity limit updates from Tetsuo Handa:
"syzbot is occasionally reporting that fuzz testing is terminated due
to hitting upper limits lockdep can track.
Analysis via /proc/lockdep* did not show any obvious culprits, allow
tuning tracing capacity constants"
* tag 'tomoyo-pr-20210426' of git://git.osdn.net/gitroot/tomoyo/tomoyo-test1:
lockdep: Allow tuning tracing capacity constants.
While this code is executed with the wait_lock held, a reader can
acquire the lock without holding wait_lock. The writer side loops
checking the value with the atomic_cond_read_acquire(), but only truly
acquires the lock when the compare-and-exchange is completed
successfully which isn’t ordered. This exposes the window between the
acquire and the cmpxchg to an A-B-A problem which allows reads
following the lock acquisition to observe values speculatively before
the write lock is truly acquired.
We've seen a problem in epoll where the reader does a xchg while
holding the read lock, but the writer can see a value change out from
under it.
Writer | Reader
--------------------------------------------------------------------------------
ep_scan_ready_list() |
|- write_lock_irq() |
|- queued_write_lock_slowpath() |
|- atomic_cond_read_acquire() |
| read_lock_irqsave(&ep->lock, flags);
--> (observes value before unlock) | chain_epi_lockless()
| | epi->next = xchg(&ep->ovflist, epi);
| | read_unlock_irqrestore(&ep->lock, flags);
| |
| atomic_cmpxchg_relaxed() |
|-- READ_ONCE(ep->ovflist); |
A core can order the read of the ovflist ahead of the
atomic_cmpxchg_relaxed(). Switching the cmpxchg to use acquire
semantics addresses this issue at which point the atomic_cond_read can
be switched to use relaxed semantics.
Fixes: b519b56e37 ("locking/qrwlock: Use atomic_cond_read_acquire() when spinning in qrwlock")
Signed-off-by: Ali Saidi <alisaidi@amazon.com>
[peterz: use try_cmpxchg()]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steve Capper <steve.capper@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Steve Capper <steve.capper@arm.com>
Pull locking fixlets from Ingo Molnar:
"Two minor fixes: one for a Clang warning, the other improves an
ambiguous/confusing kernel log message"
* tag 'locking-urgent-2021-04-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
lockdep: Address clang -Wformat warning printing for %hd
lockdep: Add a missing initialization hint to the "INFO: Trying to register non-static key" message
The indirection via a function pointer (which is at least optimized into a
tail call by the compiler) is making the code hard to read.
Clean it up and move the futex related trylock functions down to the futex
section.
Move the wake_q wakeup into rt_mutex_slowunlock(). No point in handing it
to the caller. The futex code uses a different function.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153944.247927548@linutronix.de
rtmutex is half __sched and the other half is not. If the compiler decides
to not inline larger static functions then part of the code ends up in the
regular text section.
There are also quite some performance related small helpers which are
either static or plain inline. Force inline those which make sense and mark
the rest __sched.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153944.152977820@linutronix.de
The rtmutex specific deadlock detector predates lockdep coverage of rtmutex
and since commit f5694788ad ("rt_mutex: Add lockdep annotations") it
contains a lot of redundant functionality:
- lockdep will detect an potential deadlock before rtmutex-debug
has a chance to do so
- the deadlock debugging is restricted to rtmutexes which are not
associated to futexes and have an active waiter, which is covered by
lockdep already
Remove the redundant functionality and move actual deadlock WARN() into the
deadlock code path. The latter needs a seperate cleanup.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153943.320398604@linutronix.de
The following debug members of 'struct rtmutex' are unused:
- save_state: No users
- file,line: Printed if ::name is NULL. This is only used for non-futex
locks so ::name is never NULL
- magic: Assigned to NULL by rt_mutex_destroy(), no further usage
Remove them along with unused inline and macro leftovers related to
the long gone deadlock tester.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153943.195064296@linutronix.de
Clang doesn't like format strings that truncate a 32-bit
value to something shorter:
kernel/locking/lockdep.c:709:4: error: format specifies type 'short' but the argument has type 'int' [-Werror,-Wformat]
In this case, the warning is a slightly questionable, as it could realize
that both class->wait_type_outer and class->wait_type_inner are in fact
8-bit struct members, even though the result of the ?: operator becomes an
'int'.
However, there is really no point in printing the number as a 16-bit
'short' rather than either an 8-bit or 32-bit number, so just change
it to a normal %d.
Fixes: de8f5e4f2d ("lockdep: Introduce wait-type checks")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210322115531.3987555-1-arnd@kernel.org
