From mboxrd@z Thu Jan 1 00:00:00 1970 From: Linus Torvalds Subject: Re: [PATCH] vfs: Fix RCU path walk failiures due to uninitialized nameidata seq number for root directory Date: Fri, 15 Apr 2011 14:54:23 -0700 Message-ID: References: <1302892769.2577.24.camel@schen9-DESK> <4DA8B3FB.5020401@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Tim Chen , Alexander Viro , Nick Piggin , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, shaohua.li@intel.com, alex.shi@intel.com, akpm@linux-foundation.org To: Andi Kleen Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:59257 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757077Ab1DOVzQ convert rfc822-to-8bit (ORCPT ); Fri, 15 Apr 2011 17:55:16 -0400 In-Reply-To: <4DA8B3FB.5020401@linux.intel.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Fri, Apr 15, 2011 at 2:09 PM, Andi Kleen wrote: > On 4/15/2011 11:39 AM, Tim Chen wrote: >> >> During RCU walk in path_lookupat and path_openat, the rcu lookup >> frequently failed because when root directory was looked up, seq num= ber >> was not properly set in nameidata. =A0We dropped out of RCU walk in >> nameidata_drop_rcu due to mismatch in directory entry's seq number. = =A0We >> reverted to slow path walk that need to take references. > > Thanks Tim. Adding Andrew, Linus too. IMHO this fix is quite importan= t to > actually make the fabled RCU dcache work -- without it it's just slow= er > because > it will fallback nearly allways. Well, only for absolute paths, but yes. I think all my benchmarking was for thing like "git diff", which are all about the relative paths and wouldn't have triggered this case. So this patch does look correct, and yes, should also be stable materia= l for 38. And it's pretty fundamental. But I'd like to get a few more acks exactly because it's so fundamental. Al and Nick sadly are both gone. Anybody else feel like they know something about the path lookup code? Linus -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html