Messages in this thread Patch in this message | | | Date | Tue, 8 Nov 2011 17:07:35 +0800 | From | Yong Zhang <> | Subject | Re: [PATCH 1/4] lockdep: lock_set_subclass() fix |
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On Tue, Nov 08, 2011 at 09:46:20AM +0100, Peter Zijlstra wrote: > On Tue, 2011-11-08 at 16:14 +0800, Yong Zhang wrote: > > > > But how do we deal with ->class_cache? Always set it in > > loop_up_lock_class()? > > Hrm.. good point, aside from that there's another problem as well, I > think we can deal with the cache being NULL, but is memset() an atomic > write? If not a read could observe an intermediate state and go funny.
Yup.
> > I'm tempted to go with the pure kmemcheck_mark_initialized() thing for > now.
me too :)
So something like below?
Thanks, Yong --- From: Yong Zhang <yong.zhang0@gmail.com> Subject: [PATCH] lockdep: kmemcheck: annotate ->lock in lockdep_init_map()
Since commit f59de89 [lockdep: Clear whole lockdep_map on initialization], lockdep_init_map() will clear all the struct. But it will break lock_set_class()/lock_set_subclass(). A typical race condition is like below:
CPU A CPU B lock_set_subclass(lockA); lock_set_class(lockA); lockdep_init_map(lockA); /* lockA->name is cleared */ memset(lockA); __lock_acquire(lockA); /* lockA->class_cache[] is cleared */ register_lock_class(lockA); look_up_lock_class(lockA); WARN_ON_ONCE(class->name != lock->name);
lock->name = name;
So annotate ->lock with kmemcheck_mark_initialized() to cure this problem and the one reported in commit f59de89.
Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Reported-by: Borislav Petkov <bp@alien8.de> Suggested-by: Vegard Nossum <vegard.nossum@gmail.com> Signed-off-by: Yong Zhang <yong.zhang0@gmail.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Ingo Molnar <mingo@elte.hu> Cc: Tejun Heo <tj@kernel.org> Cc: David Rientjes <rientjes@google.com> --- kernel/lockdep.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/lockdep.c b/kernel/lockdep.c index e69434b..08a2b1b 100644 --- a/kernel/lockdep.c +++ b/kernel/lockdep.c @@ -2948,7 +2948,7 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this, void lockdep_init_map(struct lockdep_map *lock, const char *name, struct lock_class_key *key, int subclass) { - memset(lock, 0, sizeof(*lock)); + kmemcheck_mark_initialized(lock, sizeof(*lock)); #ifdef CONFIG_LOCK_STAT lock->cpu = raw_smp_processor_id(); -- 1.7.5.4
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