From: Theodore Ts'o <tytso@mit.edu>
To: Zheng Liu <wenqing.lz@taobao.com>, Al Viro <viro@ZenIV.linux.org.uk>
Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] ext4: take i_mutex in ext4_symlink to eliminate a warning from ext4_truncate
Date: Thu, 28 Mar 2013 10:06:35 -0400 [thread overview]
Message-ID: <20130328140635.GA32635@thunk.org> (raw)
In-Reply-To: <20130327153506.GA4565@gmail.com>
I looked more closely at the assumption that ext4_write_begin() holds
i_mutex. This is guaranteed by Documentation/filesystems/Locking,
which notes that write_begin() and write_end() functions hold i_mutex:
PageLocked(page) i_mutex
write_begin: locks the page yes
write_end: yes, unlocks yes
So the bug is that ext4_symlink() calls __page_symlink();
__page_symlink() calls pagecache_write_begin() which calls
write_begin(), without taking i_mutex.
So we can fix this by taking i_mutex in ext4_symlink(), but I think it
would be better to take the i_mutex in __page_symlink(), since it
would then address a violation of the locking rules for all file
systems.
Al, do you agree?
- Ted
next parent reply other threads:[~2013-03-28 14:55 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1364390347-4360-1-git-send-email-wenqing.lz@taobao.com>
[not found] ` <20130327134110.GI5861@thunk.org>
[not found] ` <20130327140250.GA4316@gmail.com>
[not found] ` <20130327135155.GK5861@thunk.org>
[not found] ` <20130327150735.GA4395@gmail.com>
[not found] ` <20130327151922.GA4487@gmail.com>
[not found] ` <20130327151248.GE14900@thunk.org>
[not found] ` <20130327153506.GA4565@gmail.com>
2013-03-28 14:06 ` Theodore Ts'o [this message]
2013-04-01 15:23 ` [PATCH] fs: take i_mutex in __page_symlink() Theodore Ts'o
2013-04-01 16:35 ` Al Viro
2013-04-01 17:38 ` Theodore Ts'o
2013-04-02 8:19 ` Dmitry Monakhov
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