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Re: [btrfs/rt] lockdep false positive

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On Sun, 2017-01-22 at 18:45 +0100, Mike Galbraith wrote:
> On Sun, 2017-01-22 at 09:46 +0100, Mike Galbraith wrote:
> > Greetings btrfs/lockdep wizards,
> > 
> > RT trees have trouble with the BTRFS lockdep positive avoidance lock
> > class dance (see disk-io.c).  Seems the trouble is due to RT not having
> > a means of telling lockdep that its rwlocks are recursive for read by
> > the lock owner only, combined with the BTRFS lock class dance assuming
> > that read_lock() is annotated rwlock_acquire_read(), which RT cannot
> > do, as that would be a big fat lie.
> > 
> > Creating a rt_read_lock_shared() for btrfs_clear_lock_blocking_rw() did
> > indeed make lockdep happy as a clam for test purposes.  (hm, submitting
> > that would be excellent way to replenish frozen shark supply:)
> > 
> > Ideas?
> 
> Hrm.  The below seems to work fine, but /me strongly suspects that if
> it were this damn trivial, the issue would be long dead.

(iow, did I merely spell '2' as '3' vs creating the annotation I want)

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[btrfs/rt] lockdep false positive Mike Galbraith <umgwanakikbuti@gmail.com> - 2017-01-22 09:50 +0100
  Re: [btrfs/rt] lockdep false positive Mike Galbraith <umgwanakikbuti@gmail.com> - 2017-01-22 18:50 +0100
    Re: [btrfs/rt] lockdep false positive Mike Galbraith <umgwanakikbuti@gmail.com> - 2017-01-22 19:30 +0100
    Re: [btrfs/rt] lockdep false positive Mike Galbraith <umgwanakikbuti@gmail.com> - 2017-01-23 06:30 +0100
    Re: [btrfs/rt] lockdep false positive Peter Zijlstra <peterz@infradead.org> - 2017-01-23 10:10 +0100
    Re: [btrfs/rt] lockdep false positive Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-01-25 18:10 +0100
      Re: [btrfs/rt] lockdep false positive Mike Galbraith <umgwanakikbuti@gmail.com> - 2017-01-25 19:40 +0100
        Re: [btrfs/rt] lockdep false positive Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-01-26 18:50 +0100
          Re: [btrfs/rt] lockdep false positive Mike Galbraith <umgwanakikbuti@gmail.com> - 2017-01-26 22:00 +0100

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