linux-ext4 - Re: [URGENT PATCH] ext4: fix potential deadlock in ext4_evict

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Message-ID: <20110826155234.GC5176@thunk.org>
Date:	Fri, 26 Aug 2011 11:52:34 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Tao Ma <tm@....ma>
Cc:	Dave Chinner <david@...morbit.com>,
	Jiaying Zhang <jiayingz@...gle.com>, linux-ext4@...r.kernel.org
Subject: Re: [URGENT PATCH] ext4: fix potential deadlock in
 ext4_evict_inode()

On Fri, Aug 26, 2011 at 05:27:39PM +0800, Tao Ma wrote:
> No, it doesn't mean the ext4_truncate. But another race pasted below.
> 
> Flush inode's i_completed_io_list before calling ext4_io_wait to
> prevent the following deadlock scenario: A page fault happens while
> some process is writing inode A. During page fault,
> shrink_icache_memory is called that in turn evicts another inode
> B. Inode B has some pending io_end work so it calls ext4_ioend_wait()
> that waits for inode B's i_ioend_count to become zero. However, inode
> B's ioend work was queued behind some of inode A's ioend work on the
> same cpu's ext4-dio-unwritten workqueue. As the ext4-dio-unwritten
> thread on that cpu is processing inode A's ioend work, it tries to
> grab inode A's i_mutex lock. Since the i_mutex lock of inode A is
> still hold before the page fault happened, we enter a deadlock.

... but that shouldn't be a problem since we're not holding A's
i_mutex at this point, right?  Or am I missing something?

	   	       	       	       - Ted
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