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Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260

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On Sun, Mar 27, 2016 at 05:03:44AM -0700, Linus Torvalds wrote:
> On Sun, Mar 27, 2016 at 1:57 AM, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > I pulled ext4.git#dev on top of Linux v4.6-rc1...
> >
> > ... and did not see the call-trace.
> 
> Unless you're using overlayfs or per-file encryption, I'm not seeing
> that any of that should make any difference (but it's entirely
> possible I'm missing something).
> 
> Was it entirely repeatable before? Maybe it just happened to happen
> without that update, and then happened to _not_ happen after you
> rebooted with that 'dev' branch pulled in?
> 
> Anyway, I don't think that DEBUG_LOCKS_WARN_ON() in
> 
>   kernel/locking/lockdep.c:2017 __lock_acquire
> 

The code here is in check_no_collision(), so IIUC, there was a warning
because a real chain_key collision happened.

And chain_key is a hashsum of the ->class_idx of held_lock, calculated
via iterate_chain_key(), and the ->class_idx of a held_lock may change
from run to run IIUC, depending on the time register_lock_class() is
called for the corresponding lock class.

So this might be why Sedat didn't see the call-trace again.

Of course, I may miss something subtle here, so add the author of
check_no_collision() in CCs ;-)

If I'm right, maybe we can provide more informative dmesg here rather
than calling DEBUG_LOCKS_WARN_ON() directly?

Regards,
Boqun

> would be an ext4 issue, it looks more like an internal lockdep issue.
> 
> Adding in the lockdep people, who will set me right.
> 
>                  Linus

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Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-27 14:10 +0200
  Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Boqun Feng <boqun.feng@gmail.com> - 2016-03-27 15:40 +0200
  Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Theodore Ts'o <tytso@mit.edu> - 2016-03-27 20:30 +0200
    Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-27 21:50 +0200
      Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-27 22:30 +0200
  Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Peter Zijlstra <peterz@infradead.org> - 2016-03-27 22:50 +0200
    Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-27 23:50 +0200
    Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Peter Zijlstra <peterz@infradead.org> - 2016-03-28 08:40 +0200
    Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Ingo Molnar <mingo@kernel.org> - 2016-03-29 10:50 +0200
      Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Peter Zijlstra <peterz@infradead.org> - 2016-03-30 11:40 +0200
        Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-30 12:00 +0200
          Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Peter Zijlstra <peterz@infradead.org> - 2016-03-30 14:50 +0200
            Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-30 14:50 +0200
              Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Peter Zijlstra <peterz@infradead.org> - 2016-03-30 15:20 +0200
        Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Peter Zijlstra <peterz@infradead.org> - 2016-03-30 12:00 +0200
        Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Boqun Feng <boqun.feng@gmail.com> - 2016-03-30 12:10 +0200
          Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Peter Zijlstra <peterz@infradead.org> - 2016-03-30 12:40 +0200
            Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-30 13:10 +0200
          Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Peter Zijlstra <peterz@infradead.org> - 2016-03-31 17:50 +0200
            Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Boqun Feng <boqun.feng@gmail.com> - 2016-03-31 18:00 +0200
            Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Sedat Dilek <sedat.dilek@gmail.com> - 2016-04-02 08:30 +0200
        Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Peter Zijlstra <peterz@infradead.org> - 2016-03-30 16:10 +0200
          Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-30 17:30 +0200
            [PATCH] lockdep: print chain_key collision information Alfredo Alvarez Fernandez <alfredoalvarezfernandez@gmail.com> - 2016-03-30 19:10 +0200
              Re: [PATCH] lockdep: print chain_key collision information Peter Zijlstra <peterz@infradead.org> - 2016-03-30 19:20 +0200
              [tip:core/urgent] locking/lockdep: Print chain_key collision  information tip-bot for Alfredo Alvarez Fernandez <tipbot@zytor.com> - 2016-04-01 08:40 +0200
      Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at  kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260 Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-30 11:40 +0200

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