linux-kernel - Re: 2.6.26-rc4: RIP __call_for_each

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Message-ID: <20080605042356.GA9102@linux.vnet.ibm.com>
Date:	Wed, 4 Jun 2008 21:23:56 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	torvalds@...uxfoundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.26-rc4: RIP __call_for_each_cic+0x20/0x50

On Wed, Jun 04, 2008 at 11:32:03AM -0700, Linus Torvalds wrote:
> 
> 
> On Tue, 3 Jun 2008, Paul E. McKenney wrote:
> > 
> > The fact that put_io_context() was called from exit_io_context() means
> > that this is the last thread of a process exiting.  The fact that
> > cfq_free_io_context() was called (via cfq_dtor()) from put_io_context()
> > means that this was the last reference to the io_context.  Yet when
> > we traverse the cic_list, part of it is corrupted -- ascii "k"s through
> > RAX and RBX.
> 
> The "ascii 'k's" are just the slab POISON_FREE byte (0x6b).
> 
> IOW, something simply kfree'd the memory too early, causing the list 
> traversal to then break.

Hence the CFQ code perhaps just an innocent bystander in the wrong place
at the wrong time.  Fair enough!

							Thanx, Paul
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