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 prev parent reply other threads:[~2013-03-28 14:06 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-27 13:19 [PATCH] ext4: take i_mutex in ext4_symlink to eliminate a warning from ext4_truncate Zheng Liu
2013-03-27 13:41 ` Theodore Ts'o
2013-03-27 14:02 ` Zheng Liu
2013-03-27 13:51 ` Theodore Ts'o
2013-03-27 15:07 ` Zheng Liu
2013-03-27 15:19 ` Zheng Liu
2013-03-27 15:12 ` Theodore Ts'o
2013-03-27 15:35 ` Zheng Liu
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
2013-03-27 14:04 ` [PATCH] ext4: take i_mutex in ext4_symlink to eliminate a warning from ext4_truncate Zheng Liu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20130328140635.GA32635@thunk.org \
--to=tytso@mit.edu \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=viro@ZenIV.linux.org.uk \
--cc=wenqing.lz@taobao.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).