linux-kernel - Re: [PATCH 5/5] vfs: change nondirectory i

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Message-ID: <20120425195815.GG751@fieldses.org>
Date:	Wed, 25 Apr 2012 15:58:15 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	"J. Bruce Fields" <bfields@...hat.com>, switeho@...hat.com
Subject: Re: [PATCH 5/5] vfs: change nondirectory i_mutex ordering to fix
 quota deadlock

On Wed, Apr 25, 2012 at 09:53:43PM +0200, Jan Kara wrote:
> On Wed 25-04-12 11:28:58, J. Bruce Fields wrote:
> > On Wed, Apr 25, 2012 at 11:22:09AM -0400, bfields@...ldses.org wrote:
> > > diff --git a/fs/inode.c b/fs/inode.c
> > > index 487c924..13d23b6 100644
> > > --- a/fs/inode.c
> > > +++ b/fs/inode.c
> > > @@ -961,6 +961,17 @@ void unlock_new_inode(struct inode *inode)
> > >  }
> > >  EXPORT_SYMBOL(unlock_new_inode);
> > >  
> > > +/*
> > > + * We order !IS_NOQUOTA files before ISNOQUOTA files, and by pointer
> > > + * within each category.
> > > + */
> > > +static bool nondir_mutex_ordered(struct inode *inode1, struct inode *inode2)
> > > +{
> > > +	if (IS_NOQUOTA(inode1) == IS_NOQUOTA(inode2))
> > > +		return inode1 < inode2;
> > > +	return IS_NOQUOTA(inode2);
> > > +}
> > 
> > This seems kind of awful.  Is it what you were thinking of originally,
> > Al, and could we live with it?
>   Yeah, it's pretty ugly and also racy. I'm just now testing patches that
> would get rid of I_MUTEX_QUOTA usage for filesystems (except GFS2) and
> quota code. GFS2 could be certainly dealt with as well (at least by
> introducing a new GFS2 internal lock) so this ugly code can go away.

That would be great, thanks!

--b.
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