linux-kernel - Re: 3.6rc6 slab corruption.

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Message-ID: <CA+55aFwuO_8Wy6C7rALajiK2Pro84BrfzmKHpARx4EfG8qNMhw@mail.gmail.com>
Date:	Wed, 19 Sep 2012 10:09:45 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	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>
Subject: Re: 3.6rc6 slab corruption.

On Wed, Sep 19, 2012 at 7:00 AM, Raghavendra K T
<raghavendra.kt@...ux.vnet.ibm.com> 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);
      read(fd, buf, sizeof(buf));
   }

or similar. But it's important that they all share the same struct file.

It's also likely to make it easier to trigger the race if you have a
kernel with preemption enabled.

And you need to have SLAB debugging enabled to actually *see* the
messages. Otherwise you'll have just (possibly silent) corruption or a
memory leak.

              Linus
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