linux-kernel - Re: [PATCH v2] Fix i_mutex handling in nfsd readdir

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Date:	Wed, 22 Apr 2009 15:12:44 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	hooanon05@...oo.co.jp
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Al Viro <viro@...IV.linux.org.uk>, hch@...radead.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2] Fix i_mutex handling in nfsd readdir

On Wed, Apr 22, 2009 at 01:41:46PM +0900, hooanon05@...oo.co.jp wrote:
> 
> David Woodhouse:
> > This patch fixes it by locking the directory's i_mutex again before
> > calling the filldir functions. The original deadlocks which commit
> 	:::
> 
> An entry may be removed between the first mutex_unlock and the second
> mutex_lock. In this case, lookup_one_len() in compose_entry_fh() will
> return a negative dentry.
> Currently the inode test (positive/negative) is done AFTER fh_compose().
> Isn't it better to test it BEFORE fh_compose()?
> 
> compose_entry_fh()
> {
> 	:::
> 		dchild = lookup_one_len(name, dparent, namlen);
> 	if (IS_ERR(dchild))
> 		return 1;
> 	if (d_mountpoint(dchild) ||
> 	    fh_compose(fhp, exp, dchild, &cd->fh) != 0 ||
> 	    !dchild->d_inode)
> 		rv = 1;
> 	:::
> }

Yes, I think you're right.

Arrrgh.

--b.
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