linux-ext4 - Re: [PATCH] fs: take i_mutex in __page

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Message-ID: <20130401163538.GC21522@ZenIV.linux.org.uk>
Date:	Mon, 1 Apr 2013 17:35:38 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs: take i_mutex in __page_symlink()

On Mon, Apr 01, 2013 at 11:23:42AM -0400, Theodore Ts'o wrote:
> In Documentation/filesystems/Locking, it's documented that
> write_begin() is guaranteed to be called with i_mutex locked.  The
> function __page_symlink() was not taking i_mutex before calling
> pagecache_write_begin(), which will eventually result in the file
> system's write_begin()'s function getting called.
> 
> Other callers of pagecache_write_begin such as in fs/splice.c, call
> pagecache_write_begin() with i_mutex locked, so fix __page_symlink()
> to be consistent.
> 
> This was discovered by the addition of a new ext4 debugging assertion
> which checked to make sure i_mutex was locked before calling
> ext4_truncate().

	I doubt that it's worth doing (inode has just been created and
nobody else should have references to it - it's not fully set up, after
all)...
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