linux-kernel - Re: missing mnt_drop

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Message-Id: <E1IaSPW-0005M4-00@dorka.pomaz.szeredi.hu>
Date:	Wed, 26 Sep 2007 10:38:22 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	haveblue@...ibm.com
CC:	miklos@...redi.hu, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: missing mnt_drop_write() on open error

> On Wed, 2007-09-26 at 01:14 +0200, Miklos Szeredi wrote:
> > I get this at umount, if there was a failed open():
> > 
> > WARNING: at fs/namespace.c:586 __mntput()
> > 
> > I think the problem is that may_open() calls mnt_want_write(), but if
> > open doesn't succeed, mnt_drop_write() will not be called.
> 
> Does this help?

It didn't fix it for me, but the patch looks OK.

In __dentry_open() there's still a few places where fput() won't be
called, notably when ->open fails, which is what I'm triggering I
think.

Also even more horrible things can happen because of the
nd->intent.open.file thing.  For example if the lookup routine calls
lookup_instantiate_filp(), and after this, but before may_open() some
error happens, then release_open_intent() will call fput() on the
file, which will cause mnt_drop_write() to be called, even though a
matching mnt_want_write() hasn't yet been called.  Ugly, eh?

> I'm also thinking that we should change the open_namei*
> functions to simply return 'struct file *'.  Those are the only users
> other than NFS, and forcing the return of a file like that will force
> users to do the fput() on it if they don't want it any more.  We'd just
> need to make sure no new may_open() users pop up.  Any thoughts on that?

Yeah, something needs to be done with open, because currently it's way
too convoluted.

Miklos
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