linux-kernel - Re: [PATCH 3/5] ext4: ext4_mark_recovery_complete() doesn't need to use lock

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Date:	Sun, 26 Apr 2009 03:07:14 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH 3/5] ext4: ext4_mark_recovery_complete() doesn't need
	to use lock_super

On Sat, Apr 25, 2009 at 11:49:23PM -0400, Theodore Ts'o wrote:
> The function ext4_mark_recovery_complete() is called from two call
> paths: either (a) while mounting the filesystem, in which case there's
> no danger of any other CPU calling write_super() until the mount is
> completed, and (b) while remounting the filesystem read-write, in
> which case the fs core has already locked the superblock, and in any
> case write_super() wouldn't be called until the filesystem is
> successfully changed from being mounted read-only to read-write.

Currently ext4_remount releases/reqacquires lock_super around
ext4_mark_recovery_complete, and unfortunately currently ->write_super
can be called on a r/o filesystem (that's why we have the MS_RDONLY
checks in all instance, I plan to clean that mess up).

So for now I would keep that instance of lock_super, it'll also serve as
documentation for the locking requirements once we pushed down
lock_super to the filesystem in ->write_super and ->remount_fs so that
it can eventually be replaced with an ext4-local lock.

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