linux-kernel - Re: 3.6rc6 slab corruption.

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Date:	Wed, 19 Sep 2012 17:41:12 -0400
From:	Dave Jones <davej@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Suzuki Poulose <suzuki@...ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 3.6rc6 slab corruption.

On Wed, Sep 19, 2012 at 02:27:37PM -0700, David Rientjes wrote:
 > On Wed, 19 Sep 2012, Linus Torvalds wrote:
 > 
 > > > Create a 350 processes reading /sys/kernel/debug/kvm/spinlocks/histo_blocked
 > > > file simultaneously in while loop for more than 3 hours on my box.
 > > 
 > > You need to open the file a single time, and then after that sinelg
 > > open (either threaded or with fork()) do multiple concurrent copies
 > > something like
 > > 
 > >    for (;;) {
 > >       char buf[1024];
 > >       lseek(fd, 0, SEEK_SET);
 > 
 > These are non-seekable files, so this will always fail.  That makes the 
 > race much more difficult to trigger: the read needs to call 
 > u32_array_read() with both threads finding *ppos == 0 and then race 
 > between the kfree() and resetting of file->private_data pointer.
 > 
 >  [ I'm surprised that Dave was able to trigger this so often that he has 
 >    800MB of log. ]

Brainfart. 800Kb. Still, lots.

	Dave

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