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    SubjectRe: 3.4.4-rt13: btrfs + xfstests 006 = BOOM.. and a bonus rt_mutex deadlock report for absolutely free!
    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.


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