Hi Peter, On Mon, Aug 10, 2015 at 01:42:28PM +0200, Peter Zijlstra wrote: > On Mon, Aug 10, 2015 at 05:52:47PM +0800, Boqun Feng wrote: > > Hi Peter and Ingo, > > > > I'm now learning the code of lockdep and find that nested lock may not > > be handled correctly because we fail to take held_lock merging into > > consideration. I come up with an example and hope that could explain my > > concern. > > > > Please consider this lock/unlock sequence, I also put a patch ading this > > sequence as a test into locking-selftest: > > > > (lock_X1 and lock_X2 belong to the same lock class X, lock_Y1 belongs to > > another lock class Y) > > > > spin_lock(&lock_X1); > > spin_lock(&lock_Y1); > > spin_lock_nested_lock(&lock_X2, &lock_X1);
Sorry for the typo here.. should be spin_lock_nest_lock(). > > spin_unlock(&lock_Y1); > > spin_unlock(&lock_X2); > > spin_unlock(&lock_X1); > > > > > > This is totally legal in current lockdep rules, right? > > Yuck, I'd say no. That's quite horrible. > I admit that I didn't find this is horrible at first, but now I agree with you, this is not a rational locking order. Thank you. > Why would you ever want to do that? Though I don't want to have a locking order like that either, we can't stop others from using that order(maybe a good design review will) and lockdep yells something -unrelated- in such an order. I think we can either let lockdep complain if some one uses this locking order or clean up current code a little bit to tolarent this. If you really think we should do something about it, I can write the patch and add test cases. Thank you anyway. Regards, Boqun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
