linux-ext4 - Re: [PATCH 3/3] ext4: Fix deadlock when writing in ENOSPC conditions

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Date:	Wed, 18 Dec 2013 00:45:59 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	Akira Fujita <a-fujita@...jp.nec.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/3] ext4: Fix deadlock when writing in ENOSPC conditions

On Tue, Dec 10, 2013 at 11:14:00AM +0100, Jan Kara wrote:
> Akira-san has been reporting rare deadlocks of his machine when running
> xfstests test 269 on ext4 filesystem. The problem turned out to be in
> ext4_da_reserve_metadata() and ext4_da_reserve_space() which called
> ext4_should_retry_alloc() while holding i_data_sem. Since
> ext4_should_retry_alloc() can force a transaction commit, this is a
> lock ordering violation and leads to deadlocks.
> 
> Fix the problem by just removing the retry loops. These functions should
> just report ENOSPC to the caller (e.g. ext4_da_write_begin()) and that
> function must take care of retrying after dropping all necessary locks.
> 
> Reported-and-tested-by: Akira Fujita <a-fujita@...jp.nec.com>
> Signed-off-by: Jan Kara <jack@...e.cz>

Thanks, applied.

					- Ted
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