linux-kernel - Re: DEBUG_PAGEALLOC + order-10 alloc/free

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Message-ID: <20081226094857.GP27747@elte.hu>
Date:	Fri, 26 Dec 2008 10:48:57 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Tony Battersby <tonyb@...ernetics.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	arjan@...ux.intel.com, venkatesh.pallipadi@...el.com,
	jeremy@...p.org
Subject: Re: DEBUG_PAGEALLOC + order-10 alloc/free_pages = lockup


* Tony Battersby <tonyb@...ernetics.com> wrote:

> An order-10 alloc_pages followed by free_pages with DEBUG_PAGEALLOC
> causes a lockup during subsequent memory allocations.  Order-9 and lower
> do not trigger the problem.  This problem was introduced in 2.6.25-rc1
> and fixed in 2.6.28-rc1.  Even though the bug is now fixed, I am
> reporting it because:
> 
> 1) I am not sure that anyone ever realized that the bug existed.

Correct.

> 2) I want to make sure that the bug is really fixed and not just hidden
>    from view.

i think it got hidden. Apparently splitting up a large kernel linear page 
in IRQ context has a bug. I dont see it immediately what it could be - 
Thomas, Suresh, do you have any ideas?

> 3) To see if anyone thinks that the fix should be included in
>    2.6.27 -stable.

if 0b8fdcbcd287a1fbe66817491e6149841ae25705 applies cleanly to .27 -stable 
then i'd agree it should be added. If there's lots of dependencies then 
maybe not.

	Ingo
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