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Subject: Re: [PATCH v4 00/32] ldisc patchset
From: Peter Hurley <peter@hurleysoftware.com>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.cz>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
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        Ilya Zykov <ilya@ilyx.ru>, Dave Jones <davej@redhat.com>,
        Michael Ellerman <michael@ellerman.id.au>,
        Shawn Guo <shawn.guo@linaro.org>
Date: Thu, 21 Feb 2013 08:38:30 -0500
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On Thu, 2013-02-21 at 08:16 -0500, Sasha Levin wrote:
> On 02/20/2013 03:02 PM, Peter Hurley wrote:
> > Sasha and Dave, my trinity testbeds die in other areas right now;
> > I would really appreciate if you would please re-test this series.
> 
> Hi Peter,
> 
> I saw this twice in overnight fuzzing:
> 
> [ 1473.912280] =================================
> [ 1473.913180] [ BUG: bad contention detected! ]
> [ 1473.914071] 3.8.0-next-20130220-sasha-00038-g1ad55df-dirty #8 Tainted: G        W
> [ 1473.915684] ---------------------------------
> [ 1473.916549] kworker/1:1/361 is trying to contend lock (&tty->ldisc_sem) at:
> [ 1473.918031] [<ffffffff81c493df>] tty_ldisc_ref+0x1f/0x60
> [ 1473.919060] but there are no locks held!

Ahh, of course. That explains why the rwsem trylock doesn't track lock
stats -- because by the time lock_contended() is called, up_write()
could have just called lockdep_release(), so that it appears as if the
lock has been released when in fact it has not but is about to.

I'll just remove the lock contention test from the trylocks.

Thanks,
Peter

> [ 1473.919813]
> [ 1473.919813] other info that might help us debug this:
> [ 1473.920044] 2 locks held by kworker/1:1/361:
> [ 1473.920044]  #0:  (events){.+.+.+}, at: [<ffffffff811328a8>] process_one_work+0x228/0x6a0
> [ 1473.920044]  #1:  ((&buf->work)){+.+...}, at: [<ffffffff811328a8>] process_one_work+0x228/0x6a0
> [ 1473.920044]
> [ 1473.920044] stack backtrace:
> [ 1473.920044] Pid: 361, comm: kworker/1:1 Tainted: G        W    3.8.0-next-20130220-sasha-00038-g1ad55df-dirty #8
> [ 1473.920044] Call Trace:
> [ 1473.920044]  [<ffffffff81c493df>] ? tty_ldisc_ref+0x1f/0x60
> [ 1473.920044]  [<ffffffff81182026>] print_lock_contention_bug+0xf6/0x110
> [ 1473.920044]  [<ffffffff81184973>] lock_contended+0x213/0x4e0
> [ 1473.920044]  [<ffffffff81c4bb41>] ldsem_down_read_trylock+0xb1/0xc0
> [ 1473.920044]  [<ffffffff81c493df>] tty_ldisc_ref+0x1f/0x60
> [ 1473.920044]  [<ffffffff81c4a687>] flush_to_ldisc+0x37/0x1a0
> [ 1473.920044]  [<ffffffff811329e6>] process_one_work+0x366/0x6a0
> [ 1473.920044]  [<ffffffff811328a8>] ? process_one_work+0x228/0x6a0
> [ 1473.920044]  [<ffffffff811332a8>] worker_thread+0x238/0x370
> [ 1473.920044]  [<ffffffff81133070>] ? rescuer_thread+0x310/0x310
> [ 1473.920044]  [<ffffffff8113d873>] kthread+0xe3/0xf0
> [ 1473.920044]  [<ffffffff8113d790>] ? flush_kthread_work+0x1f0/0x1f0
> [ 1473.920044]  [<ffffffff83dab4fc>] ret_from_fork+0x7c/0xb0
> [ 1473.920044]  [<ffffffff8113d790>] ? flush_kthread_work+0x1f0/0x1f0
> 
> 
> Thanks,
> Sasha