On Sun, Mar 15, 2015 at 11:49:07PM +0200, Matthias Bonne wrote:
So the counter is set to 1 before taking the spinlock, which I think
might cause the race. Did I miss something?
Yes, you miss the fact that __mutex_slowpath_needs_to_unlock() is 0 for
the CONFIG_DEBUG_MUTEXES case:
# 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
# undef __mutex_slowpath_needs_to_unlock
# define __mutex_slowpath_needs_to_unlock() 0