linux-kernel - Re: [BUG?] possible recursive locking detected

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Date:	Thu, 27 Jul 2006 00:24:32 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	eike-kernel@...tec.de, linux-kernel@...r.kernel.org,
	aia21@...tab.net
Subject: Re: [BUG?] possible recursive locking detected

On Thu, 27 Jul 2006 16:51:29 +1000
Nick Piggin <nickpiggin@...oo.com.au> wrote:

> > We hold the ext2 directory mutex, and ntfs_put_inode is trying to take an
> > ntfs i_mutex.  Not a deadlock as such, but it could become one in ntfs if
> > ntfs ever does a __GFP_WAIT allocation inside i_mutex, which it surely
> > does.
> 
> Though it should be using GFP_NOFS, right? So the dcache shrinker would
> not reenter the fs in that case.

Sort-of, arguably.  Many years ago, holding i_mutex (i_sem) was considered
to be "in the fs" and one should use GFP_NOFS.

(This code dates from the ext2 directory-in-pagecache conversion - it's
2.4 stuff.)

It's better, of course, to use GFP_HIGHUSER for pagecache so we should aim
to get this working.  And that means don't-take-i_mutex-on-the-reclaim-path.

We quite possibly are doing that in other places, too.

> I'm surprised ext2 is allocating with __GFP_FS set, though. Would that
> cause any problem?

It might, if ext2 takes i_mutex on the reclaim path.  But it doesn't.

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