hung_task: show the blocker task if the task is hung on mutex

Patch series "hung_task: Dump the blocking task stacktrace", v4.

The hung_task detector is very useful for detecting the lockup. Howev

hung_task: show the blocker task if the task is hung on mutex

Patch series "hung_task: Dump the blocking task stacktrace", v4.

The hung_task detector is very useful for detecting the lockup. However,
since it only dumps the blocked (uninterruptible sleep) processes, it is
not enough to identify the root cause of that lockup.

For example, if a process holds a mutex and sleep an event in
interruptible state long time, the other processes will wait on the mutex
in uninterruptible state. In this case, the waiter processes are dumped,
but the blocker process is not shown because it is sleep in interruptible
state.

This adds a feature to dump the blocker task which holds a mutex
when detecting a hung task. e.g.

INFO: task cat:115 blocked for more than 122 seconds.
Not tainted 6.14.0-rc3-00003-ga8946be3de00 #156
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:cat state:D stack:13432 pid:115 tgid:115 ppid:106 task_flags:0x400100 flags:0x00000002
Call Trace:
<TASK>
__schedule+0x731/0x960
? schedule_preempt_disabled+0x54/0xa0
schedule+0xb7/0x140
? __mutex_lock+0x51b/0xa60
? __mutex_lock+0x51b/0xa60
schedule_preempt_disabled+0x54/0xa0
__mutex_lock+0x51b/0xa60
read_dummy+0x23/0x70
full_proxy_read+0x6a/0xc0
vfs_read+0xc2/0x340
? __pfx_direct_file_splice_eof+0x10/0x10
? do_sendfile+0x1bd/0x2e0
ksys_read+0x76/0xe0
do_syscall_64+0xe3/0x1c0
? exc_page_fault+0xa9/0x1d0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x4840cd
RSP: 002b:00007ffe99071828 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004840cd
RDX: 0000000000001000 RSI: 00007ffe99071870 RDI: 0000000000000003
RBP: 00007ffe99071870 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000001000000 R11: 0000000000000246 R12: 0000000000001000
R13: 00000000132fd3a0 R14: 0000000000000001 R15: ffffffffffffffff
</TASK>
INFO: task cat:115 is blocked on a mutex likely owned by task cat:114.
task:cat state:S stack:13432 pid:114 tgid:114 ppid:106 task_flags:0x400100 flags:0x00000002
Call Trace:
<TASK>
__schedule+0x731/0x960
? schedule_timeout+0xa8/0x120
schedule+0xb7/0x140
schedule_timeout+0xa8/0x120
? __pfx_process_timeout+0x10/0x10
msleep_interruptible+0x3e/0x60
read_dummy+0x2d/0x70
full_proxy_read+0x6a/0xc0
vfs_read+0xc2/0x340
? __pfx_direct_file_splice_eof+0x10/0x10
? do_sendfile+0x1bd/0x2e0
ksys_read+0x76/0xe0
do_syscall_64+0xe3/0x1c0
? exc_page_fault+0xa9/0x1d0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x4840cd
RSP: 002b:00007ffe3e0147b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004840cd
RDX: 0000000000001000 RSI: 00007ffe3e014800 RDI: 0000000000000003
RBP: 00007ffe3e014800 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000001000000 R11: 0000000000000246 R12: 0000000000001000
R13: 000000001a0a93a0 R14: 0000000000000001 R15: ffffffffffffffff
</TASK>

TBD: We can extend this feature to cover other locks like rwsem and
rt_mutex, but rwsem requires to dump all the tasks which acquire and wait
that rwsem. We can follow the waiter link but the output will be a bit
different compared with mutex case.


This patch (of 2):

The "hung_task" shows a long-time uninterruptible slept task, but most
often, it's blocked on a mutex acquired by another task. Without dumping
such a task, investigating the root cause of the hung task problem is very
difficult.

This introduce task_struct::blocker_mutex to point the mutex lock which
this task is waiting for. Since the mutex has "owner" information, we can
find the owner task and dump it with hung tasks.

Note: the owner can be changed while dumping the owner task, so
this is "likely" the owner of the mutex.

With this change, the hung task shows blocker task's info like below;

INFO: task cat:115 blocked for more than 122 seconds.
Not tainted 6.14.0-rc3-00003-ga8946be3de00 #156
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:cat state:D stack:13432 pid:115 tgid:115 ppid:106 task_flags:0x400100 flags:0x00000002
Call Trace:
<TASK>
__schedule+0x731/0x960
? schedule_preempt_disabled+0x54/0xa0
schedule+0xb7/0x140
? __mutex_lock+0x51b/0xa60
? __mutex_lock+0x51b/0xa60
schedule_preempt_disabled+0x54/0xa0
__mutex_lock+0x51b/0xa60
read_dummy+0x23/0x70
full_proxy_read+0x6a/0xc0
vfs_read+0xc2/0x340
? __pfx_direct_file_splice_eof+0x10/0x10
? do_sendfile+0x1bd/0x2e0
ksys_read+0x76/0xe0
do_syscall_64+0xe3/0x1c0
? exc_page_fault+0xa9/0x1d0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x4840cd
RSP: 002b:00007ffe99071828 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004840cd
RDX: 0000000000001000 RSI: 00007ffe99071870 RDI: 0000000000000003
RBP: 00007ffe99071870 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000001000000 R11: 0000000000000246 R12: 0000000000001000
R13: 00000000132fd3a0 R14: 0000000000000001 R15: ffffffffffffffff
</TASK>
INFO: task cat:115 is blocked on a mutex likely owned by task cat:114.
task:cat state:S stack:13432 pid:114 tgid:114 ppid:106 task_flags:0x400100 flags:0x00000002
Call Trace:
<TASK>
__schedule+0x731/0x960
? schedule_timeout+0xa8/0x120
schedule+0xb7/0x140
schedule_timeout+0xa8/0x120
? __pfx_process_timeout+0x10/0x10
msleep_interruptible+0x3e/0x60
read_dummy+0x2d/0x70
full_proxy_read+0x6a/0xc0
vfs_read+0xc2/0x340
? __pfx_direct_file_splice_eof+0x10/0x10
? do_sendfile+0x1bd/0x2e0
ksys_read+0x76/0xe0
do_syscall_64+0xe3/0x1c0
? exc_page_fault+0xa9/0x1d0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x4840cd
RSP: 002b:00007ffe3e0147b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004840cd
RDX: 0000000000001000 RSI: 00007ffe3e014800 RDI: 0000000000000003
RBP: 00007ffe3e014800 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000001000000 R11: 0000000000000246 R12: 0000000000001000
R13: 000000001a0a93a0 R14: 0000000000000001 R15: ffffffffffffffff
</TASK>

[[email protected]: implement debug_show_blocker() in C rather than in CPP]
Link: https://lkml.kernel.org/r/174046694331.2194069.15472952050240807469.stgit@mhiramat.tok.corp.google.com
Link: https://lkml.kernel.org/r/174046695384.2194069.16796289525958195643.stgit@mhiramat.tok.corp.google.com
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Reviewed-by: Lance Yang <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Joel Granados <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Tomasz Figa <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yongliang Gao <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

show more ...

locking/mutex: Add MUTEX_WARN_ON() into fast path

Scenario: In platform_device_register, the driver misuses struct
device as platform_data, making kmemdup duplicate a device. Accessing
the duplicate

locking/mutex: Add MUTEX_WARN_ON() into fast path

Scenario: In platform_device_register, the driver misuses struct
device as platform_data, making kmemdup duplicate a device. Accessing
the duplicate may cause list corruption due to its mutex magic or list
holding old content.
It recurs randomly as the first mutex - getting process skips the slow
path and mutex check. Adding MUTEX_WARN_ON(lock->magic!= lock) in
__mutex_trylock_fast() makes it always happen.

Signed-off-by: Yunhui Cui <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

show more ...

sched/wake_q: Add helper to call wake_up_q after unlock with preemption disabled

A common pattern seen when wake_qs are used to defer a wakeup
until after a lock is released is something like:
pre

sched/wake_q: Add helper to call wake_up_q after unlock with preemption disabled

A common pattern seen when wake_qs are used to defer a wakeup
until after a lock is released is something like:
preempt_disable();
raw_spin_unlock(lock);
wake_up_q(wake_q);
preempt_enable();

So create some raw_spin_unlock*_wake() helper functions to clean
this up.

Applies on top of the fix I submitted here:
https://lore.kernel.org/lkml/[email protected]/

NOTE: I recognise the unlock()/unlock_irq()/unlock_irqrestore()
variants creates its own duplication, which we could use a macro
to generate the similar functions, but I often dislike how those
generation macros making finding the actual implementation
harder, so I left the three functions as is. If folks would
prefer otherwise, let me know and I'll switch it.

Suggested-by: Peter Zijlstra <[email protected]>
Signed-off-by: John Stultz <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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locking/mutex: Expose __mutex_owner()

Implementing proxy execution requires that scheduler code be able to
identify the current owner of a mutex. Expose __mutex_owner() for
this purpose (alone!). In

locking/mutex: Expose __mutex_owner()

Implementing proxy execution requires that scheduler code be able to
identify the current owner of a mutex. Expose __mutex_owner() for
this purpose (alone!). Includes a null mutex check, so that users
of the function can be simplified.

[Removed the EXPORT_SYMBOL]
[jstultz: Reworked per Peter's suggestions]
Signed-off-by: Juri Lelli <[email protected]>
Signed-off-by: Valentin Schneider <[email protected]>
Signed-off-by: Connor O'Brien <[email protected]>
Signed-off-by: John Stultz <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Metin Kaya <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
Tested-by: K Prateek Nayak <[email protected]>
Tested-by: Metin Kaya <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/mutex: Make mutex::wait_lock irq safe

With the proxy-execution series, we traverse the task->mutex->task
blocked_on/owner chain in the scheduler core. We do this while holding
the rq::lock t

locking/mutex: Make mutex::wait_lock irq safe

With the proxy-execution series, we traverse the task->mutex->task
blocked_on/owner chain in the scheduler core. We do this while holding
the rq::lock to keep the structures in place while taking and
releasing the alternating lock types.

Since the mutex::wait_lock is one of the locks we will take in this
way under the rq::lock in the scheduler core, we need to make sure
that its usage elsewhere is irq safe.

[rebase & fix {un,}lock_wait_lock helpers in ww_mutex.h]
Signed-off-by: Juri Lelli <[email protected]>
Signed-off-by: Connor O'Brien <[email protected]>
Signed-off-by: John Stultz <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Metin Kaya <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
Tested-by: K Prateek Nayak <[email protected]>
Tested-by: Metin Kaya <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/mutex: Remove wakeups from under mutex::wait_lock

In preparation to nest mutex::wait_lock under rq::lock we need
to remove wakeups from under it.

Do this by utilizing wake_qs to defer the w

locking/mutex: Remove wakeups from under mutex::wait_lock

In preparation to nest mutex::wait_lock under rq::lock we need
to remove wakeups from under it.

Do this by utilizing wake_qs to defer the wakeup until after the
lock is dropped.

[Heavily changed after 55f036ca7e74 ("locking: WW mutex cleanup") and
08295b3b5bee ("locking: Implement an algorithm choice for Wound-Wait
mutexes")]
[jstultz: rebased to mainline, added extra wake_up_q & init
to avoid hangs, similar to Connor's rework of this patch]

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Juri Lelli <[email protected]>
Signed-off-by: John Stultz <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Metin Kaya <[email protected]>
Acked-by: Davidlohr Bueso <[email protected]>
Tested-by: K Prateek Nayak <[email protected]>
Tested-by: Metin Kaya <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/mutex: Document that mutex_unlock() is non-atomic

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.

Th

locking/mutex: Document that mutex_unlock() is non-atomic

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 <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking: export contention tracepoints for bcachefs six locks

The bcachefs implementation of six locks is intended to land in
generic locking code in the long term, but has been pulled into the
bcac

locking: export contention tracepoints for bcachefs six locks

The bcachefs implementation of six locks is intended to land in
generic locking code in the long term, but has been pulled into the
bcachefs subsystem for internal use for the time being. This code
lift breaks the bcachefs module build as six locks depend a couple
of the generic locking tracepoints. Export these tracepoint symbols
for bcachefs.

Signed-off-by: Brian Foster <[email protected]>
Signed-off-by: Kent Overstreet <[email protected]>

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locking/mutex: Make contention tracepoints more consistent wrt adaptive spinning

Have the trace_contention_*() tracepoints consistently include
adaptive spinning. In order to differentiate between t

locking/mutex: Make contention tracepoints more consistent wrt adaptive spinning

Have the trace_contention_*() tracepoints consistently include
adaptive spinning. In order to differentiate between the spinning and
non-spinning states add LCB_F_MUTEX and combine with LCB_F_SPIN.

The consequence is that a mutex contention can now triggler multiple
_begin() tracepoints before triggering an _end().

Additionally, this fixes one path where mutex would trigger _end()
without ever seeing a _begin().

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>

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locking: Apply contention tracepoints in the slow path

Adding the lock contention tracepoints in various lock function slow
paths. Note that each arch can define spinlock differently, I only
added

locking: Apply contention tracepoints in the slow path

Adding the lock contention tracepoints in various lock function slow
paths. Note that each arch can define spinlock differently, I only
added it only to the generic qspinlock for now.

Signed-off-by: Namhyung Kim <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Hyeonggon Yoo <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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locking: Add lock contention tracepoints

This adds two new lock contention tracepoints like below:

* lock:contention_begin
* lock:contention_end

The lock:contention_begin takes a flags argument

locking: Add lock contention tracepoints

This adds two new lock contention tracepoints like below:

* lock:contention_begin
* lock:contention_end

The lock:contention_begin takes a flags argument to classify locks. I
found it useful to identify what kind of locks it's tracing like if
it's spinning or sleeping, reader-writer lock, real-time, and per-cpu.

Move tracepoint definitions into mutex.c so that we can use them
without lockdep.

Signed-off-by: Namhyung Kim <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Hyeonggon Yoo <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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locking: Make owner_on_cpu() into <linux/sched.h>

Move the owner_on_cpu() from kernel/locking/rwsem.c into
include/linux/sched.h with under CONFIG_SMP, then use it
in the mutex/rwsem/rtmutex to simp

locking: Make owner_on_cpu() into <linux/sched.h>

Move the owner_on_cpu() from kernel/locking/rwsem.c into
include/linux/sched.h with under CONFIG_SMP, then use it
in the mutex/rwsem/rtmutex to simplify the code.

Signed-off-by: Kefeng Wang <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking: Remove rcu_read_{,un}lock() for preempt_{dis,en}able()

preempt_disable/enable() is equal to RCU read-side crital section, and
the spinning codes in mutex and rwsem could ensure that the pre

locking: Remove rcu_read_{,un}lock() for preempt_{dis,en}able()

preempt_disable/enable() is equal to RCU read-side crital section, and
the spinning codes in mutex and rwsem could ensure that the preemption
is disabled. So let's remove the unnecessary rcu_read_lock/unlock for
saving some cycles in hot codes.

Signed-off-by: Yanfei Xu <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Waiman Long <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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kernel/locking: Add context to ww_mutex_trylock()

i915 will soon gain an eviction path that trylock a whole lot of locks
for eviction, getting dmesg failures like below:

BUG: MAX_LOCK_DEPTH too l

kernel/locking: Add context to ww_mutex_trylock()

i915 will soon gain an eviction path that trylock a whole lot of locks
for eviction, getting dmesg failures like below:

BUG: MAX_LOCK_DEPTH too low!
turning off the locking correctness validator.
depth: 48 max: 48!
48 locks held by i915_selftest/5776:
#0: ffff888101a79240 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x88/0x160
#1: ffffc900009778c0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_vma_pin.constprop.63+0x39/0x1b0 [i915]
#2: ffff88800cf74de8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_vma_pin.constprop.63+0x5f/0x1b0 [i915]
#3: ffff88810c7f9e38 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x1c4/0x9d0 [i915]
#4: ffff88810bad5768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
#5: ffff88810bad60e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
...
#46: ffff88811964d768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
#47: ffff88811964e0e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
INFO: lockdep is turned off.

Fixing eviction to nest into ww_class_acquire is a high priority, but
it requires a rework of the entire driver, which can only be done one
step at a time.

As an intermediate solution, add an acquire context to
ww_mutex_trylock, which allows us to do proper nesting annotations on
the trylocks, making the above lockdep splat disappear.

This is also useful in regulator_lock_nested, which may avoid dropping
regulator_nesting_mutex in the uncontended path, so use it there.

TTM may be another user for this, where we could lock a buffer in a
fastpath with list locks held, without dropping all locks we hold.

[peterz: rework actual ww_mutex_trylock() implementations]
Signed-off-by: Maarten Lankhorst <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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locking/ww_mutex: Initialize waiter.ww_ctx properly

The consolidation of the debug code for mutex waiter intialization sets
waiter::ww_ctx to a poison value unconditionally. For regular mutexes this

locking/ww_mutex: Initialize waiter.ww_ctx properly

The consolidation of the debug code for mutex waiter intialization sets
waiter::ww_ctx to a poison value unconditionally. For regular mutexes this
is intended to catch the case where waiter_ww_ctx is dereferenced
accidentally.

For ww_mutex the poison value has to be overwritten either with a context
pointer or NULL for ww_mutexes without context.

The rework broke this as it made the store conditional on the context
pointer instead of the argument which signals whether ww_mutex code should
be compiled in or optiized out. As a result waiter::ww_ctx ends up with the
poison pointer for contextless ww_mutexes which causes a later dereference of
the poison pointer because it is != NULL.

Use the build argument instead so for ww_mutex the poison value is always
overwritten.

Fixes: c0afb0ffc06e6 ("locking/ww_mutex: Gather mutex_waiter initialization")
Reported-by: Guenter Roeck <[email protected]>
Suggested-by: Peter Zijlstra <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/rtmutex: Add mutex variant for RT

Add the necessary defines, helpers and API functions for replacing struct mutex on
a PREEMPT_RT enabled kernel with an rtmutex based variant.

No functional

locking/rtmutex: Add mutex variant for RT

Add the necessary defines, helpers and API functions for replacing struct mutex on
a PREEMPT_RT enabled kernel with an rtmutex based variant.

No functional change when CONFIG_PREEMPT_RT=n

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/ww_mutex: Split out the W/W implementation logic into kernel/locking/ww_mutex.h

Split the W/W mutex helper functions out into a separate header file, so
they can be shared with a rtmutex bas

locking/ww_mutex: Split out the W/W implementation logic into kernel/locking/ww_mutex.h

Split the W/W mutex helper functions out into a separate header file, so
they can be shared with a rtmutex based variant later.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/ww_mutex: Split up ww_mutex_unlock()

Split the ww related part out into a helper function so it can be reused
for a rtmutex based ww_mutex implementation.

[ mingo: Fixed bisection failure.

locking/ww_mutex: Split up ww_mutex_unlock()

Split the ww related part out into a helper function so it can be reused
for a rtmutex based ww_mutex implementation.

[ mingo: Fixed bisection failure. ]

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/ww_mutex: Gather mutex_waiter initialization

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (I

locking/ww_mutex: Gather mutex_waiter initialization

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/ww_mutex: Simplify lockdep annotations

No functional change.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by:

locking/ww_mutex: Simplify lockdep annotations

No functional change.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/mutex: Make mutex::wait_lock raw

The wait_lock of mutex is really a low level lock. Convert it to a
raw_spinlock like the wait_lock of rtmutex.

[ mingo: backmerged the test_lockup.c build f

locking/mutex: Make mutex::wait_lock raw

The wait_lock of mutex is really a low level lock. Convert it to a
raw_spinlock like the wait_lock of rtmutex.

[ mingo: backmerged the test_lockup.c build fix by bigeasy. ]

Co-developed-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/mutex: Consolidate core headers, remove kernel/locking/mutex-debug.h

Having two header files which contain just the non-debug and debug variants
is mostly waste of disc space and has no real

locking/mutex: Consolidate core headers, remove kernel/locking/mutex-debug.h

Having two header files which contain just the non-debug and debug variants
is mostly waste of disc space and has no real value. Stick the debug
variants into the common mutex.h file as counterpart to the stubs for the
non-debug case.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/mutex: Add MUTEX_WARN_ON

Cleanup some #ifdef'fery.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Reviewed-by: Yanfei Xu <yanfei.

locking/mutex: Add MUTEX_WARN_ON

Cleanup some #ifdef'fery.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Reviewed-by: Yanfei Xu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/mutex: Introduce __mutex_trylock_or_handoff()

Yanfei reported that it is possible to loose HANDOFF when we race with
mutex_unlock() and end up setting HANDOFF on an unlocked mutex. At
that p

locking/mutex: Introduce __mutex_trylock_or_handoff()

Yanfei reported that it is possible to loose HANDOFF when we race with
mutex_unlock() and end up setting HANDOFF on an unlocked mutex. At
that point anybody can steal it, losing HANDOFF in the process.

If this happens often enough, we can in fact starve the top waiter.

Solve this by folding the 'set HANDOFF' operation into the trylock
operation, such that either we acquire the lock, or it gets HANDOFF
set. This avoids having HANDOFF set on an unlocked mutex.

Reported-by: Yanfei Xu <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Reviewed-by: Yanfei Xu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/mutex: Fix HANDOFF condition

Yanfei reported that setting HANDOFF should not depend on recomputing
@first, only on @first state. Which would then give:

if (ww_ctx || !first)
first = _

locking/mutex: Fix HANDOFF condition

Yanfei reported that setting HANDOFF should not depend on recomputing
@first, only on @first state. Which would then give:

if (ww_ctx || !first)
first = __mutex_waiter_is_first(lock, &waiter);
if (first)
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);

But because 'ww_ctx || !first' is basically 'always' and the test for
first is relatively cheap, omit that first branch entirely.

Reported-by: Yanfei Xu <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Reviewed-by: Yanfei Xu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

show more ...