linux-kernel - Re: rcu_prempt stalls / lockup

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Message-ID: <20140402224840.GA5385@redhat.com>
Date:	Wed, 2 Apr 2014 18:48:40 -0400
From:	Dave Jones <davej@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: rcu_prempt stalls / lockup

On Wed, Apr 02, 2014 at 09:20:43AM -0700, Paul E. McKenney wrote:
 > On Tue, Apr 01, 2014 at 11:32:45AM -0700, Paul E. McKenney wrote:
 > > On Tue, Apr 01, 2014 at 02:04:14PM -0400, Dave Jones wrote:
 > > > On Tue, Apr 01, 2014 at 10:55:45AM -0700, Paul E. McKenney wrote:
 > 
 > [ . . . ]
 > 
 > > >  > Waiting uninterruptibly.  Presumably blocked on mutex_lock().  But
 > > >  > you have CONFIG_PROVE_LOCKING(), so any deadlocks should have been
 > > >  > reported.
 > > > 
 > > > Lockdep had reported something a little earlier (timestamped at 1108.xxxxxx)
 > > > but that's a known false-positive in xfs.
 > > 
 > > Yep, I would be very surprised if that was related to the grace-period hang.
 > 
 > Ah, but it could be suppressing later lockdep splats.  So if this can be
 > reproduced without xfs, we might get additional information from lockdep.

Hrmph.

$ git bisect bad
The merge base 5cb480f6b488128140c940abff3c36f524a334a8 is bad.
This means the bug has been fixed between 5cb480f6b488128140c940abff3c36f524a334a8 and [455c6fdbd219161bd09b1165f11699d6d73de11c 62c206bd514600d4d73751ade00dca8e488390a3 e086481baf9d0436bdd6e9b739bfa4a83fb89ef5].

Not sure where to go from here..

The 'good' news is I can reproduce it pretty reliably now.
I start my fuzz tester, and immediately do a git diff in my working tree,
and then boom..

	Dave

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