locking/ww_mutex: Gather mutex_waiter initialization

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (I

locking/ww_mutex: Gather mutex_waiter initialization

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.281927514@linutronix.de

show more ...

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 <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.995350521@linutronix.de

show more ...

locking/mutex: clear MUTEX_FLAGS if wait_list is empty due to signal

When a interruptible mutex locker is interrupted by a signal
without acquiring this lock and removed from the wait queue.
if the

locking/mutex: clear MUTEX_FLAGS if wait_list is empty due to signal

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: 040a0a371005 ("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

show more ...

locking/mutex: clear MUTEX_FLAGS if wait_list is empty due to signal

[ Upstream commit 3a010c493271f04578b133de977e0e5dd2848cea ]

When a interruptible mutex locker is interrupted by a signal
withou

locking/mutex: clear MUTEX_FLAGS if wait_list is empty due to signal

[ Upstream commit 3a010c493271f04578b133de977e0e5dd2848cea ]

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: 040a0a371005 ("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
Signed-off-by: Sasha Levin <sashal@kernel.org>

show more ...

lockdep: Introduce wait-type checks

Extend lockdep to validate lock wait-type context.

The current wait-types are:

LD_WAIT_FREE, /* wait free, rcu etc.. */
LD_WAIT_SPIN, /* spin loops, raw_spi

lockdep: Introduce wait-type checks

Extend lockdep to validate lock wait-type context.

The current wait-types are:

LD_WAIT_FREE, /* wait free, rcu etc.. */
LD_WAIT_SPIN, /* spin loops, raw_spinlock_t etc.. */
LD_WAIT_CONFIG, /* CONFIG_PREEMPT_LOCK, spinlock_t etc.. */
LD_WAIT_SLEEP, /* sleeping locks, mutex_t etc.. */

Where lockdep validates that the current lock (the one being acquired)
fits in the current wait-context (as generated by the held stack).

This ensures that there is no attempt to acquire mutexes while holding
spinlocks, to acquire spinlocks while holding raw_spinlocks and so on. In
other words, its a more fancy might_sleep().

Obviously RCU made the entire ordeal more complex than a simple single
value test because RCU can be acquired in (pretty much) any context and
while it presents a context to nested locks it is not the same as it
got acquired in.

Therefore its necessary to split the wait_type into two values, one
representing the acquire (outer) and one representing the nested context
(inner). For most 'normal' locks these two are the same.

[ To make static initialization easier we have the rule that:
.outer == INV means .outer == .inner; because INV == 0. ]

It further means that its required to find the minimal .inner of the held
stack to compare against the outer of the new lock; because while 'normal'
RCU presents a CONFIG type to nested locks, if it is taken while already
holding a SPIN type it obviously doesn't relax the rules.

Below is an example output generated by the trivial test code:

raw_spin_lock(&foo);
spin_lock(&bar);
spin_unlock(&bar);
raw_spin_unlock(&foo);

[ BUG: Invalid wait context ]
-----------------------------
swapper/0/1 is trying to lock:
ffffc90000013f20 (&bar){....}-{3:3}, at: kernel_init+0xdb/0x187
other info that might help us debug this:
1 lock held by swapper/0/1:
#0: ffffc90000013ee0 (&foo){+.+.}-{2:2}, at: kernel_init+0xd1/0x187

The way to read it is to look at the new -{n,m} part in the lock
description; -{3:3} for the attempted lock, and try and match that up to
the held locks, which in this case is the one: -{2,2}.

This tells that the acquiring lock requires a more relaxed environment than
presented by the lock stack.

Currently only the normal locks and RCU are converted, the rest of the
lockdep users defaults to .inner = INV which is ignored. More conversions
can be done when desired.

The check for spinlock_t nesting is not enabled by default. It's a separate
config option for now as there are known problems which are currently
addressed. The config option allows to identify these problems and to
verify that the solutions found are indeed solving them.

The config switch will be removed and the checks will permanently enabled
once the vast majority of issues has been addressed.

[ bigeasy: Move LD_WAIT_FREE,… out of CONFIG_LOCKDEP to avoid compile
failure with CONFIG_DEBUG_SPINLOCK + !CONFIG_LOCKDEP]
[ tglx: Add the config option ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113242.427089655@linutronix.de

show more ...

locking/mutex: Replace spin_is_locked() with lockdep

lockdep_assert_held() is better suited to checking locking requirements,
since it only checks if the current thread holds the lock regardless of

locking/mutex: Replace spin_is_locked() with lockdep

lockdep_assert_held() is better suited to checking locking requirements,
since it only checks if the current thread holds the lock regardless of
whether someone else does. This is also a step towards possibly removing
spin_is_locked().

Signed-off-by: Lance Roy <ldr709@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

show more ...

locking/mutex: Rework mutex::owner

The current mutex implementation has an atomic lock word and a
non-atomic owner field.

This disparity leads to a number of issues with the current mutex code
as i

locking/mutex: Rework mutex::owner

The current mutex implementation has an atomic lock word and a
non-atomic owner field.

This disparity leads to a number of issues with the current mutex code
as it means that we can have a locked mutex without an explicit owner
(because the owner field has not been set, or already cleared).

This leads to a number of weird corner cases, esp. between the
optimistic spinning and debug code. Where the optimistic spinning
code needs the owner field updated inside the lock region, the debug
code is more relaxed because the whole lock is serialized by the
wait_lock.

Also, the spinning code itself has a few corner cases where we need to
deal with a held lock without an owner field.

Furthermore, it becomes even more of a problem when trying to fix
starvation cases in the current code. We end up stacking special case
on special case.

To solve this rework the basic mutex implementation to be a single
atomic word that contains the owner and uses the low bits for extra
state.

This matches how PI futexes and rt_mutex already work. By having the
owner an integral part of the lock state a lot of the problems
dissapear and we get a better option to deal with starvation cases,
direct owner handoff.

Changing the basic mutex does however invalidate all the arch specific
mutex code; this patch leaves that unused in-place, a later patch will
remove that.

Tested-by: Jason Low <jason.low2@hpe.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

show more ...

locking: avoid passing around 'thread_info' in mutex debugging code

None of the code actually wants a thread_info, it all wants a
task_struct, and it's just converting back and forth between the two

locking: avoid passing around 'thread_info' in mutex debugging code

None of the code actually wants a thread_info, it all wants a
task_struct, and it's just converting back and forth between the two
("ti->task" to get the task_struct from the thread_info, and
"task_thread_info(task)" to go the other way).

No semantic change.

Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

show more ...

mutex: Always clear owner field upon mutex_unlock()

Currently if DEBUG_MUTEXES is enabled, the mutex->owner field is only
cleared iff debug_locks is active. This exposes a race to other users of
the

mutex: Always clear owner field upon mutex_unlock()

Currently if DEBUG_MUTEXES is enabled, the mutex->owner field is only
cleared iff debug_locks is active. This exposes a race to other users of
the field where the mutex->owner may be still set to a stale value,
potentially upsetting mutex_spin_on_owner() among others.

References: https://bugs.freedesktop.org/show_bug.cgi?id=87955
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1420540175-30204-1-git-send-email-chris@chris-wilson.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>

show more ...

locking/mutex: Fix debug_mutexes

debug_mutex_unlock() would bail when !debug_locks and forgets to
actually unlock.

Reported-by: "Michael L. Semon" <mlsemon35@gmail.com>
Reported-by: "Kirill A. Shut

locking/mutex: Fix debug_mutexes

debug_mutex_unlock() would bail when !debug_locks and forgets to
actually unlock.

Reported-by: "Michael L. Semon" <mlsemon35@gmail.com>
Reported-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Fixes: 6f008e72cd11 ("locking/mutex: Fix debug checks")
Tested-by: Dave Jones <davej@redhat.com>
Cc: Jason Low <jason.low2@hp.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140410141559.GE13658@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

show more ...

locking/mutex: Fix debug checks

OK, so commit:

1d8fe7dc8078 ("locking/mutexes: Unlock the mutex without the wait_lock")

generates this boot warning when CONFIG_DEBUG_MUTEXES=y:

WARNING: CPU:

locking/mutex: Fix debug checks

OK, so commit:

1d8fe7dc8078 ("locking/mutexes: Unlock the mutex without the wait_lock")

generates this boot warning when CONFIG_DEBUG_MUTEXES=y:

WARNING: CPU: 0 PID: 139 at /usr/src/linux-2.6/kernel/locking/mutex-debug.c:82 debug_mutex_unlock+0x155/0x180() DEBUG_LOCKS_WARN_ON(lock->owner != current)

And that makes sense, because as soon as we release the lock a
new owner can come in...

One would think that !__mutex_slowpath_needs_to_unlock()
implementations suffer the same, but for DEBUG we fall back to
mutex-null.h which has an unconditional 1 for that.

The mutex debug code requires the mutex to be unlocked after
doing the debug checks, otherwise it can find inconsistent
state.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: jason.low2@hp.com
Link: http://lkml.kernel.org/r/20140312122442.GB27965@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

show more ...

mutexes: Give more informative mutex warning in the !lock->owner case

When mutex debugging is enabled and an imbalanced mutex_unlock()
is called, we get the following, slightly confusing warning:

mutexes: Give more informative mutex warning in the !lock->owner case

When mutex debugging is enabled and an imbalanced mutex_unlock()
is called, we get the following, slightly confusing warning:

[ 364.208284] DEBUG_LOCKS_WARN_ON(lock->owner != current)

But in that case the warning is due to an imbalanced mutex_unlock() call,
and the lock->owner is NULL - so the message is misleading.

So improve the message by testing for this case specifically:

DEBUG_LOCKS_WARN_ON(!lock->owner)

Signed-off-by: Liu, Chuansheng <chuansheng.liu@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1386136693.3650.48.camel@cliu38-desktop-build
[ Improved the changelog, changed the patch to use !lock->owner consistently. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

show more ...

locking: Move the mutex code to kernel/locking/

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-1ditvncg30dgbpvrz

locking: Move the mutex code to kernel/locking/

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-1ditvncg30dgbpvrz2bxfmke@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

show more ...

locking/mutex: clear MUTEX_FLAGS if wait_list is empty due to signal

[ Upstream commit 3a010c493271f04578b133de977e0e5dd2848cea ]

When a interruptible mutex locker is interrupted by

locking/mutex: clear MUTEX_FLAGS if wait_list is empty due to signal

[ Upstream commit 3a010c493271f04578b133de977e0e5dd2848cea ]

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: 040a0a371005 ("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
Signed-off-by: Sasha Levin <sashal@kernel.org>

show more ...

lockdep: Introduce wait-type checks

Extend lockdep to validate lock wait-type context.

The current wait-types are:

LD_WAIT_FREE, /* wait free, rcu etc.. *

lockdep: Introduce wait-type checks

Extend lockdep to validate lock wait-type context.

The current wait-types are:

LD_WAIT_FREE, /* wait free, rcu etc.. */
LD_WAIT_SPIN, /* spin loops, raw_spinlock_t etc.. */
LD_WAIT_CONFIG, /* CONFIG_PREEMPT_LOCK, spinlock_t etc.. */
LD_WAIT_SLEEP, /* sleeping locks, mutex_t etc.. */

Where lockdep validates that the current lock (the one being acquired)
fits in the current wait-context (as generated by the held stack).

This ensures that there is no attempt to acquire mutexes while holding
spinlocks, to acquire spinlocks while holding raw_spinlocks and so on. In
other words, its a more fancy might_sleep().

Obviously RCU made the entire ordeal more complex than a simple single
value test because RCU can be acquired in (pretty much) any context and
while it presents a context to nested locks it is not the same as it
got acquired in.

Therefore its necessary to split the wait_type into two values, one
representing the acquire (outer) and one representing the nested context
(inner). For most 'normal' locks these two are the same.

[ To make static initialization easier we have the rule that:
.outer == INV means .outer == .inner; because INV == 0. ]

It further means that its required to find the minimal .inner of the held
stack to compare against the outer of the new lock; because while 'normal'
RCU presents a CONFIG type to nested locks, if it is taken while already
holding a SPIN type it obviously doesn't relax the rules.

Below is an example output generated by the trivial test code:

raw_spin_lock(&foo);
spin_lock(&bar);
spin_unlock(&bar);
raw_spin_unlock(&foo);

[ BUG: Invalid wait context ]
-----------------------------
swapper/0/1 is trying to lock:
ffffc90000013f20 (&bar){....}-{3:3}, at: kernel_init+0xdb/0x187
other info that might help us debug this:
1 lock held by swapper/0/1:
#0: ffffc90000013ee0 (&foo){+.+.}-{2:2}, at: kernel_init+0xd1/0x187

The way to read it is to look at the new -{n,m} part in the lock
description; -{3:3} for the attempted lock, and try and match that up to
the held locks, which in this case is the one: -{2,2}.

This tells that the acquiring lock requires a more relaxed environment than
presented by the lock stack.

Currently only the normal locks and RCU are converted, the rest of the
lockdep users defaults to .inner = INV which is ignored. More conversions
can be done when desired.

The check for spinlock_t nesting is not enabled by default. It's a separate
config option for now as there are known problems which are currently
addressed. The config option allows to identify these problems and to
verify that the solutions found are indeed solving them.

The config switch will be removed and the checks will permanently enabled
once the vast majority of issues has been addressed.

[ bigeasy: Move LD_WAIT_FREE,… out of CONFIG_LOCKDEP to avoid compile
failure with CONFIG_DEBUG_SPINLOCK + !CONFIG_LOCKDEP]
[ tglx: Add the config option ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113242.427089655@linutronix.de

show more ...

locking/mutex: Replace spin_is_locked() with lockdep

lockdep_assert_held() is better suited to checking locking requirements,
since it only checks if the current thread holds the lock re

locking/mutex: Replace spin_is_locked() with lockdep

lockdep_assert_held() is better suited to checking locking requirements,
since it only checks if the current thread holds the lock regardless of
whether someone else does. This is also a step towards possibly removing
spin_is_locked().

Signed-off-by: Lance Roy <ldr709@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

show more ...

locking/mutex: Rework mutex::owner

The current mutex implementation has an atomic lock word and a
non-atomic owner field.

This disparity leads to a number of issues with the cur

locking/mutex: Rework mutex::owner

The current mutex implementation has an atomic lock word and a
non-atomic owner field.

This disparity leads to a number of issues with the current mutex code
as it means that we can have a locked mutex without an explicit owner
(because the owner field has not been set, or already cleared).

This leads to a number of weird corner cases, esp. between the
optimistic spinning and debug code. Where the optimistic spinning
code needs the owner field updated inside the lock region, the debug
code is more relaxed because the whole lock is serialized by the
wait_lock.

Also, the spinning code itself has a few corner cases where we need to
deal with a held lock without an owner field.

Furthermore, it becomes even more of a problem when trying to fix
starvation cases in the current code. We end up stacking special case
on special case.

To solve this rework the basic mutex implementation to be a single
atomic word that contains the owner and uses the low bits for extra
state.

This matches how PI futexes and rt_mutex already work. By having the
owner an integral part of the lock state a lot of the problems
dissapear and we get a better option to deal with starvation cases,
direct owner handoff.

Changing the basic mutex does however invalidate all the arch specific
mutex code; this patch leaves that unused in-place, a later patch will
remove that.

Tested-by: Jason Low <jason.low2@hpe.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

show more ...

locking: avoid passing around 'thread_info' in mutex debugging code

None of the code actually wants a thread_info, it all wants a
task_struct, and it's just converting back and forth bet

locking: avoid passing around 'thread_info' in mutex debugging code

None of the code actually wants a thread_info, it all wants a
task_struct, and it's just converting back and forth between the two
("ti->task" to get the task_struct from the thread_info, and
"task_thread_info(task)" to go the other way).

No semantic change.

Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

show more ...

mutex: Always clear owner field upon mutex_unlock()

Currently if DEBUG_MUTEXES is enabled, the mutex->owner field is only
cleared iff debug_locks is active. This exposes a race to other

mutex: Always clear owner field upon mutex_unlock()

Currently if DEBUG_MUTEXES is enabled, the mutex->owner field is only
cleared iff debug_locks is active. This exposes a race to other users of
the field where the mutex->owner may be still set to a stale value,
potentially upsetting mutex_spin_on_owner() among others.

References: https://bugs.freedesktop.org/show_bug.cgi?id=87955
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1420540175-30204-1-git-send-email-chris@chris-wilson.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>

show more ...

locking/mutex: Fix debug_mutexes

debug_mutex_unlock() would bail when !debug_locks and forgets to
actually unlock.

Reported-by: "Michael L. Semon" <mlsemon35@gmail.com>
Repo

locking/mutex: Fix debug_mutexes

debug_mutex_unlock() would bail when !debug_locks and forgets to
actually unlock.

Reported-by: "Michael L. Semon" <mlsemon35@gmail.com>
Reported-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Fixes: 6f008e72cd11 ("locking/mutex: Fix debug checks")
Tested-by: Dave Jones <davej@redhat.com>
Cc: Jason Low <jason.low2@hp.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140410141559.GE13658@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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locking/mutex: Fix debug checks

OK, so commit:

1d8fe7dc8078 ("locking/mutexes: Unlock the mutex without the wait_lock")

generates this boot warning when CONFIG_DEBUG_MUTE

locking/mutex: Fix debug checks

OK, so commit:

1d8fe7dc8078 ("locking/mutexes: Unlock the mutex without the wait_lock")

generates this boot warning when CONFIG_DEBUG_MUTEXES=y:

WARNING: CPU: 0 PID: 139 at /usr/src/linux-2.6/kernel/locking/mutex-debug.c:82 debug_mutex_unlock+0x155/0x180() DEBUG_LOCKS_WARN_ON(lock->owner != current)

And that makes sense, because as soon as we release the lock a
new owner can come in...

One would think that !__mutex_slowpath_needs_to_unlock()
implementations suffer the same, but for DEBUG we fall back to
mutex-null.h which has an unconditional 1 for that.

The mutex debug code requires the mutex to be unlocked after
doing the debug checks, otherwise it can find inconsistent
state.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: jason.low2@hp.com
Link: http://lkml.kernel.org/r/20140312122442.GB27965@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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mutexes: Give more informative mutex warning in the !lock->owner case

When mutex debugging is enabled and an imbalanced mutex_unlock()
is called, we get the following, slightly confusing

mutexes: Give more informative mutex warning in the !lock->owner case

When mutex debugging is enabled and an imbalanced mutex_unlock()
is called, we get the following, slightly confusing warning:

[ 364.208284] DEBUG_LOCKS_WARN_ON(lock->owner != current)

But in that case the warning is due to an imbalanced mutex_unlock() call,
and the lock->owner is NULL - so the message is misleading.

So improve the message by testing for this case specifically:

DEBUG_LOCKS_WARN_ON(!lock->owner)

Signed-off-by: Liu, Chuansheng <chuansheng.liu@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1386136693.3650.48.camel@cliu38-desktop-build
[ Improved the changelog, changed the patch to use !lock->owner consistently. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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locking: Move the mutex code to kernel/locking/

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-1

locking: Move the mutex code to kernel/locking/

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-1ditvncg30dgbpvrz2bxfmke@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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