linux-kernel - Re: 3.14.0+/x86: lockdep and mutexes not getting along

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Message-ID: <20140410081348.GJ10526@twins.programming.kicks-ass.net>
Date:	Thu, 10 Apr 2014 10:13:48 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	"Michael L. Semon" <mlsemon35@...il.com>,
	Ingo Molnar <mingo@...nel.org>, jason.low2@...com,
	linux-kernel@...r.kernel.org
Subject: Re: 3.14.0+/x86: lockdep and mutexes not getting along

On Wed, Apr 09, 2014 at 03:19:40PM +0300, Kirill A. Shutemov wrote:
> On Sun, Apr 06, 2014 at 01:12:14AM -0400, Michael L. Semon wrote:
> > Hi!  Starting early in this merge window for 3.15, lockdep has been
> > giving me trouble.  Normally, a splat will happen, lockdep will shut
> > itself off, and my i686 Pentium 4 PC will continue.  Now, after the
> > splat, it will allow one key of input at either a VGA console or over
> > serial.  After that, only the magic SysRq keys and KDB still work.
> > File activity stops, and many processes are stuck in the D state.
> > 
> > Bisect brought me here:
> > 
> > root@...earer:/usr/src/kernel-git/linux# git bisect good
> > 6f008e72cd111a119b5d8de8c5438d892aae99eb is the first bad commit
> > commit 6f008e72cd111a119b5d8de8c5438d892aae99eb
> > Author: Peter Zijlstra <peterz@...radead.org>
> > Date:   Wed Mar 12 13:24:42 2014 +0100
> > 
> >     locking/mutex: Fix debug checks
> > 
> >     OK, so commit:
> > 
> >       1d8fe7dc8078 ("locking/mutexes: Unlock the mutex without the wait_lock")
> > 
> >     generates this boot warning when CONFIG_DEBUG_MUTEXES=y:
> > 
> >       WARNING: CPU: 0 PID: 139 at /usr/src/linux-2.6/kernel/locking/mutex-debug.c:82 debug_mutex_unlock+0x155/0x180() DEBUG_LOCKS_WARN_ON(lock->owner != current)
> > 
> >     And that makes sense, because as soon as we release the lock a
> >     new owner can come in...
> > 
> >     One would think that !__mutex_slowpath_needs_to_unlock()
> >     implementations suffer the same, but for DEBUG we fall back to
> >     mutex-null.h which has an unconditional 1 for that.
> > 
> >     The mutex debug code requires the mutex to be unlocked after
> >     doing the debug checks, otherwise it can find inconsistent
> >     state.
> > 
> >     Reported-by: Ingo Molnar <mingo@...nel.org>
> >     Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> >     Cc: jason.low2@...com
> >     Link: http://lkml.kernel.org/r/20140312122442.GB27965@twins.programming.kicks-ass.net
> >     Signed-off-by: Ingo Molnar <mingo@...nel.org>
> > 
> > :040000 040000 80e40c2009942a31f98127c4f9fa958f34b3947b f46ed4b70c4f30fc665fe8f810d3c13920cd765a M      kernel
> > 
> > Indeed, my issues are solved (so far) simply by reverting this commit.
> > 
> > Might someone test lockdep on x86 to see if this is a consistent
> > issue that needs to be adjusted?  My lockdep splats are generated by
> > running xfstests test generic/113 on XFS, but splats caused by other
> > issues should still create the same symptoms.
> > 
> > Otherwise, this 3.15 kernel has been rather kind to me so far.
> > 
> > PC is an i686 Pentium 4 with 1280 MB RAM and old IDE hardware,
> > running Slackware 14.1.

So what does lockdep say when it messes up your p4? 

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