From: Theodore Tso <tytso@mit.edu>
To: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, Greg Kroah-Hartman <gregkh@suse.de>,
Kay Sievers <kay.sievers@vrfy.org>
Subject: Re: Lockdep problem involving sysfs_mutex in ext4 in linux-next
Date: Fri, 20 Mar 2009 18:44:58 -0400 [thread overview]
Message-ID: <20090320224458.GC4559@mit.edu> (raw)
In-Reply-To: <20090320222522.GB4559@mit.edu>
On Fri, Mar 20, 2009 at 06:25:22PM -0400, Theodore Tso wrote:
> So if I'm reading this right, the problem is happening because
> someplace in the kernel, fs/sysfs code is grabbing mmap_sem while it
> is holding sysfs_mutex, right? But I can't see where that might be
> happening...
Never mind, I see it. sysfs_readdir() calls filldir() while holding
sysfs_mutex, and filldir() in turn calls copy_to_user(), which can
grab mmap_sem.
The problem is that in other code paths, mmap_sem() is grabbed while
we grab inode->i_alloc_sem() (in ext4_page_mkwrite), and that in turns
has a dependency on jbd2_handle, which has a dependency on s_lock, and
hence lock_super(). Ugh. What a mess.
- Ted
prev parent reply other threads:[~2009-03-20 22:45 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-14 14:02 Lockdep problem involving sysfs_mutex in ext4 in linux-next Theodore Ts'o
2009-03-14 23:05 ` Peter Zijlstra
2009-03-20 22:25 ` Theodore Tso
2009-03-20 22:44 ` Theodore Tso [this message]
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