linux-ext4 - [Bug 15018] ext4 backtraces out of nowhere

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Message-Id: <201001182306.o0IN68F9004917@demeter.kernel.org>
Date:	Mon, 18 Jan 2010 23:06:08 GMT
From:	bugzilla-daemon@...zilla.kernel.org
To:	linux-ext4@...r.kernel.org
Subject: [Bug 15018] ext4 backtraces out of nowhere

http://bugzilla.kernel.org/show_bug.cgi?id=15018


Jan Kara <jack@...e.cz> changed:

           What    |Removed                     |Added
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                 CC|                            |jack@...e.cz, tytso@....edu




--- Comment #2 from Jan Kara <jack@...e.cz>  2010-01-18 23:06:07 ---
Ah, inlining and such stuff made reading this stack trace quite difficult.
Anyway, the problem is that we just should not call write_inode_now() in
ext4_da_reserve_space() when we have transaction already started. And as
Andreas correctly points out, the patch even introduces a deadlock because it
can call write_inode_now with wait==1. Moreover we hold page lock when holding
write_inode_now which introduces a plenty of nasty locking issues I believe.
The bug has been introduced by commit 0637c6f4135f592f094207c7c21e7c0fc5557834.

Ted, I think that if we are failing to do the write because of ENOSPC, the only
reasonable non-deadlocky thing to do is to restart the write completely - i.e.,
bail out up to ext4_da_write_begin, stop the transaction, drop the page, *do
some magic*, and start again...

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