On Fri, 2012-07-13 at 11:52 +0200, Thomas Gleixner wrote: > On Fri, 13 Jul 2012, Mike Galbraith wrote: > > On Thu, 2012-07-12 at 15:31 +0200, Thomas Gleixner wrote: > > > Bingo, that makes it more likely that this is caused by copying w/o > > > initializing the lock and then freeing the original structure. > > > > > > A quick check for memcpy finds that __btrfs_close_devices() does a > > > memcpy of btrfs_device structs w/o initializing the lock in the new > > > copy, but I have no idea whether that's the place we are looking for. > > > > Thanks a bunch Thomas. I doubt I would have ever figured out that lala > > land resulted from _copying_ a lock. That's one I won't be forgetting > > any time soon. Box not only survived a few thousand xfstests 006 runs, > > dbench seemed disinterested in deadlocking virgin 3.0-rt. > > Cute. It think that the lock copying caused the deadlock problem as > the list pointed to the wrong place, so we might have ended up with > following down the wrong chain when walking the list as long as the > original struct was not freed. That beast is freed under RCU so there > could be a rcu read side critical section fiddling with the old lock > and cause utter confusion. Virgin 3.0-rt appears to really be solid. But then it doesn't have pesky rwlocks. > /me goes and writes a nastigram^W proper changelog > > > btrfs still locks up in my enterprise kernel, so I suppose I had better > > plug your fix into 3.4-rt and see what happens, and go beat hell out of > > virgin 3.0-rt again to be sure box really really survives dbench. > > A test against 3.4-rt sans enterprise mess might be nice as well. Enterprise is 3.0-stable with um 555 btrfs patches (oh dear). Virgin 3.4-rt and 3.2-rt deadlock gripe. Enterprise doesn't gripe, but deadlocks, so I have another adventure in my future even if I figure out wth to do about rwlocks. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
