linux-kernel - Re: [PATCH 1/2] kill-the-bkl/reiserfs: acquire the inode mutex safely

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Date:	Fri, 29 May 2009 22:23:44 -0600
From:	"Trenton D. Adams" <trenton.d.adams@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Reiserfs <reiserfs-devel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Jeff Mahoney <jeffm@...e.com>,
	Chris Mason <chris.mason@...cle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Alexander Beregalov <a.beregalov@...il.com>
Subject: Re: [PATCH 1/2] kill-the-bkl/reiserfs: acquire the inode mutex safely

On Fri, May 29, 2009 at 9:22 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> On Fri, May 29, 2009 at 09:05:31PM -0600, Trenton D. Adams wrote:
>> On Sat, May 16, 2009 at 12:02 PM, Frederic Weisbecker
>> <fweisbec@...il.com> wrote:
>> > While searching a pathname, an inode mutex can be acquired
>> > in do_lookup() which calls reiserfs_lookup() which in turn
>> > acquires the write lock.
>> >
>> > On the other side reiserfs_fill_super() can acquire the write_lock
>> > and then call reiserfs_lookup_privroot() which can acquire an
>> > inode mutex (the root of the mount point).
>> >
>> > So we theoretically risk an AB - BA lock inversion that could lead
>> > to a deadlock.
>> >
>> > As for other lock dependencies found since the bkl to mutex
>> > conversion, the fix is to use reiserfs_mutex_lock_safe() which
>> > drops the lock dependency to the write lock.
>> >
>>
>> I'm curious, did this get applied, and is it related to the following?
>>  I was having these in 2.6.30-rc3.  I am now on 2.6.30-rc7 as of
>> today.  I haven't seen them today.  But then again, I only seen this
>> happen one time.
>
>
> Hi,
>
> No, may be it will come for 2.6.31 but for now it is not merged so
> it's not related.
>
> If you see such warning anymore, don't hesitate to tell about
> it!
>
> Thanks!
>

I was trying to imply that the patch might fix the problem I saw, not
that it was the cause.  I only though that because it mentioned a
potential deadlock, and it seems like that is what the problem I saw
was.
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