On (08/05/11 14:36), Peter Zijlstra wrote: > The below is what I've come up with. > Hello, I think that should work. Will test, anyway. Thanks, Sergey > --- > Subject: lockdep: Fix wrong assumption in match_held_lock > From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > Date: Fri Aug 05 14:26:17 CEST 2011 > > match_held_lock() was assuming it was being called on a lock class > that had already seen usage. > > This condition was true for bug-free code using lockdep_assert_held(), > since you're in fact holding the lock when calling it. However the > assumption fails the moment you assume the assertion can fail, which > is the whole point of having the assertion in the first place. > > Anyway, now that there's more lockdep_is_held() users, notably > __rcu_dereference_check(), its much easier to trigger this since we > test for a number of locks and we only need to hold any one of them to > be good. > > Reported-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > --- > kernel/lockdep.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > Index: linux-2.6/kernel/lockdep.c > =================================================================== > --- linux-2.6.orig/kernel/lockdep.c > +++ linux-2.6/kernel/lockdep.c > @@ -3111,7 +3111,13 @@ static int match_held_lock(struct held_l > if (!class) > class = look_up_lock_class(lock, 0); > > - if (DEBUG_LOCKS_WARN_ON(!class)) > + /* > + * If look_up_lock_class() failed to find a class, we're trying > + * to test if we hold a lock that has never yet been acquired. > + * Clearly if the lock hasn't been acquired _ever_, we're not > + * holding it either, so report failure. > + */ > + if (!class) > return 0; > > if (DEBUG_LOCKS_WARN_ON(!hlock->nest_lock)) > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>