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Commit 6f008e72 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

locking/mutex: Fix debug checks 



OK, so commit:

  1d8fe7dc ("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: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent 34c6bc2c

kernel/locking/mutex-debug.c

+6 −0
Original line number Original line Diff line number Diff line
@@ -83,6 +83,12 @@ void debug_mutex_unlock(struct mutex *lock) 




	DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);

	DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);

	mutex_clear_owner(lock);

	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,

void debug_mutex_init(struct mutex *lock, const char *name,

kernel/locking/mutex.c

+7 −0
Original line number Original line Diff line number Diff line
@@ -34,6 +34,13 @@ 
#ifdef CONFIG_DEBUG_MUTEXES

#ifdef CONFIG_DEBUG_MUTEXES

# include "mutex-debug.h"

# include "mutex-debug.h"

# include <asm-generic/mutex-null.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

#else

# include "mutex.h"

# include "mutex.h"

# include <asm/mutex.h>

# include <asm/mutex.h>