From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [PATCH] Fix i_mutex handling in nfsd readdir. Date: Sun, 19 Apr 2009 08:18:49 +0100 Message-ID: <1240125529.3589.44.camel@macbook.infradead.org> References: <8036.1237474444@jrobl> <1237475837.16359.106.camel@macbook.infradead.org> <8913.1237476890@jrobl> <1239960739.3428.33.camel@macbook.infradead.org> <20090417193233.GM26366@ZenIV.linux.org.uk> <1240006620.19059.41.camel@macbook.infradead.org> <20090417224350.GN26366@ZenIV.linux.org.uk> <20090417225306.GO26366@ZenIV.linux.org.uk> <1240013753.21423.86.camel@macbook.infradead.org> <905.1240024314@jrobl> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Al Viro , bfields@citi.umich.edu, hch@infradead.org, "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" To: hooanon05@yahoo.co.jp Return-path: Received: from casper.infradead.org ([85.118.1.10]:47045 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751156AbZDSHS5 (ORCPT ); Sun, 19 Apr 2009 03:18:57 -0400 In-Reply-To: <905.1240024314@jrobl> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Sat, 2009-04-18 at 12:11 +0900, hooanon05@yahoo.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 > > 14f7dd63 was designed to avoid are still avoided, because they were due > > to fs-internal locking, not i_mutex. > ::: > > --- a/fs/namei.c > > +++ b/fs/namei.c > > @@ -1248,6 +1248,8 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len) > > int err; > > struct qstr this; > > > > + WARN_ON_ONCE(!mutex_is_locked(&base->d_inode->i_mutex)); > > + > > err = __lookup_one_len(name, &this, base, len); > > I'd suggest this checking is done only when CONFIG_DEBUG_KERNEL (or > something) is enabled. Because unconditional checking costs high for the > well-reviewed lookup code. It's supposed to be locked. It's likely to have been locked quite recently, so it'll be in the cache. I don't think the mutex_is_locked() check is going to be that expensive, is it? -- David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation