From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sedat Dilek Subject: Re: [PATCH] vfs: Fix RCU path walk failiures due to uninitialized nameidata seq number for root directory Date: Sat, 16 Apr 2011 07:43:52 +0200 Message-ID: References: <1302892769.2577.24.camel@schen9-DESK> <4DA8B3FB.5020401@linux.intel.com> Reply-To: sedat.dilek@gmail.com Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Andi Kleen , 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: Linus Torvalds Return-path: Received: from mail-qw0-f46.google.com ([209.85.216.46]:59043 "EHLO mail-qw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751088Ab1DPFnx convert rfc822-to-8bit (ORCPT ); Sat, 16 Apr 2011 01:43:53 -0400 In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Fri, Apr 15, 2011 at 11:54 PM, Linus Torvalds wrote: > On Fri, Apr 15, 2011 at 2:09 PM, Andi Kleen wrot= e: >> 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 nu= mber >>> was not properly set in nameidata. =C2=A0We dropped out of RCU walk= in >>> nameidata_drop_rcu due to mismatch in directory entry's seq number.= =C2=A0We >>> reverted to slow path walk that need to take references. >> >> Thanks Tim. Adding Andrew, Linus too. IMHO this fix is quite importa= nt to >> actually make the fabled RCU dcache work -- without it it's just slo= wer >> 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 mater= ial 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= ? > > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 =C2=A0 =C2=A0 Linus > I see this patch was pushed. What's with fs-synchronize_rcu-when-unregister_filesystem-success-not-f= ailure.patch from [1]? - Sedat - [1] https://patchwork.kernel.org/patch/707322/ -- 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