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locking/mutex: Fix debug checks

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OK, so commit:

  1d8fe7dc80 ("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>
This commit is contained in:
Peter Zijlstra 2014-03-12 13:24:42 +01:00 committed by Ingo Molnar
parent 34c6bc2c91
commit 6f008e72cd
2 changed files with 13 additions and 0 deletions
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6
kernel/locking/mutex-debug.c
View file

@ -83,6 +83,12 @@ void debug_mutex_unlock(struct mutex *lock)
DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
mutex_clear_owner(lock);
/*
* __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug
* mutexes so that we can do it here after we've verified state.
*/
atomic_set(&lock->count, 1);
}
void debug_mutex_init(struct mutex *lock, const char *name,

7
kernel/locking/mutex.c
View file

@ -34,6 +34,13 @@
#ifdef CONFIG_DEBUG_MUTEXES
# include "mutex-debug.h"
# include <asm-generic/mutex-null.h>
/*
* Must be 0 for the debug case so we do not do the unlock outside of the
* wait_lock region. debug_mutex_unlock() will do the actual unlock in this
* case.
*/
# undef __mutex_slowpath_needs_to_unlock
# define __mutex_slowpath_needs_to_unlock() 0
#else
# include "mutex.h"
# include <asm/mutex.h>