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    SubjectRe: regression 4.4: deadlock in with cgroup percpu_rwsem
    On Mon, Jan 18, 2016 at 07:48:16PM +0100, Christian Borntraeger wrote:
    > On 01/18/2016 07:32 PM, Peter Zijlstra wrote:
    > > On Fri, Jan 15, 2016 at 04:13:34PM +0100, Christian Borntraeger wrote:
    > >>> Yes, the deadlock is gone and the system is still running.
    > >>> After some time I had the following WARN in the logs, though.
    > >>> Not sure yet if that is related.
    > >>>
    > >>> [25331.763607] DEBUG_LOCKS_WARN_ON(lock->owner != current)
    > >>> [25331.763630] ------------[ cut here ]------------
    > >>> [25331.763634] WARNING: at kernel/locking/mutex-debug.c:80
    > >
    > >> I restarted the test with panic_on_warn. Hopefully I can get a dump to check
    > >> which mutex this was.
    > >
    > > Hard to reproduce warnings like this tend to point towards memory
    > > corruption. Someone stepped on the mutex value and tickles the sanity
    > > check.
    > >
    > > With lockdep and debugging enabled the mutex gets quite a bit bigger, so
    > > it gets more likely to be hit by 'random' corruption.
    > >
    > > The locking in seq_read() seems rather straight forward.
    >
    > I was able to reproduce. The dump shows a mutex that has an owner field, which
    > does not exists as a task so this all looks fishy. The good thing is, that I
    > can reproduce the issue within some hours. (exact same backtrace). Will add some
    > more debug data to get a handle where we come from.

    Did the owner field show to something that still looks like a task_struct?


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