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

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Message-ID: <20090530134132.GA5969@nowhere>
Date:	Sat, 30 May 2009 15:41:33 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Trenton D. Adams" <trenton.d.adams@...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 10:23:44PM -0600, Trenton D. Adams wrote:
> 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.


Ah ok. No it's part of a tree which reworks the reiserfs locking scheme
by removing the old one based on the legacy and obsolete bkl (big kernel
lock). In this tree I had to fix several deadlocks or at least unsafe
lock states because the bkl is converted into a mutex and some new lock
dependencies were borned after that. But these issues had nothing
to deal with upstream problems.

BTW, would you be interested in giving a try with this reiserfs bkl
removal tree? I really lack testing and feedbacks from users.

Thanks!

Frederic.

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