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

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Date:	Wed, 22 Apr 2009 13:41:46 +0900
From:	hooanon05@...oo.co.jp
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Al Viro <viro@...IV.linux.org.uk>, bfields@...i.umich.edu,
	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 


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;
	:::
}


J. R. Okajima
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