linux-kernel - Re: [PATCH] mm: fix lazy vmap purging (use-after-free error)

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Date:	Fri, 20 Feb 2009 15:01:57 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Vegard Nossum <vegard.nossum@...il.com>, stable@...nel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: fix lazy vmap purging (use-after-free error)


* Ingo Molnar <mingo@...e.hu> wrote:

> ah, indeed:
> 
>         list_del_rcu(&va->list);
> 
> i suspect it could be hit big time in a workload that opens 
> more than 512 files, as expand_files() uses a 
> vmalloc()+vfree() pair in that case.

hm, perhaps it's not a problem after all. The freeing is done 
via rcu, and list_del_rcu() leaves the forward pointer intact.

So how did it happen that the entry got kfree()d before the loop 
was done? We are in a spinlocked section so the CPU should not 
have entered rcu processing.

	Ingo
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