From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752151AbbEGRjm (ORCPT ); Thu, 7 May 2015 13:39:42 -0400 Received: from smtprelay0216.hostedemail.com ([216.40.44.216]:56172 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751651AbbEGRjj (ORCPT ); Thu, 7 May 2015 13:39:39 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::,RULES_HIT:41:355:379:541:599:960:968:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1542:1593:1594:1711:1730:1747:1777:1792:1801:2393:2553:2559:2562:2693:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4250:4605:5007:6261:7875:7903:8660:10004:10400:10848:10967:11026:11232:11473:11658:11914:12043:12438:12517:12519:12555:12740:13019:13148:13161:13229:13230:13870:21080,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: room26_36d30bd9a2b15 X-Filterd-Recvd-Size: 3211 Date: Thu, 7 May 2015 13:39:35 -0400 From: Steven Rostedt To: Al Viro Cc: David Howells , LKML , linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] VFS: Add back check for !inode in walk_component() Message-ID: <20150507133935.2d2e3181@gandalf.local.home> In-Reply-To: <20150507172834.GD889@ZenIV.linux.org.uk> References: <20150507125241.4da739ac@gandalf.local.home> <20150507172834.GD889@ZenIV.linux.org.uk> X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 7 May 2015 18:28:34 +0100 Al Viro wrote: > On Thu, May 07, 2015 at 12:52:41PM -0400, Steven Rostedt wrote: > > > > Commit 698934df8b45 "VFS: Combine inode checks with d_is_negative() and > > d_is_positive() in pathwalk" removed a check for inode being NULL in > > walk_component() where the type is tested. Stressing my tracefs create > > and remove instances while reading the files now triggers this: > > So you get NULL ->d_inode with stale flags? The thing is, ->d_inode > becoming NULL should happen via d_delete(), which goes throug this: But it's not the delete, it's the creation of a new d_entry. Pehaps it gets linked premature? The tracing I had happened in tracefs_create_file(). > unsigned flags = READ_ONCE(dentry->d_flags); > > flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU); > WRITE_ONCE(dentry->d_flags, flags); > smp_wmb(); > dentry->d_inode = NULL; > > and after that assignment to ->d_flags you'll see d_is_negative() being > true. OTOH, we have > *inode = dentry->d_inode; > if (read_seqcount_retry(&dentry->d_seq, seq)) > in lookup_fast(), and read_seqcount_retry() is > { > smp_rmb(); > return __read_seqcount_retry(s, start); > } > > IOW, we have smp_rmb() between fetching ->d_inode and checking ->d_flags. > > If you can reproduce that at will, could you make it dump nd->flags along with > dentry involved? I had them printed in my previous traces. The flags were 0x200088, and they were 0 just before the call. ftrace-test-mki-3201 [000] 85.306761: bprint: walk_component: inode=(nil) dentry=0xee3c0240 neg:1 ftrace-test-mki-3201 [000] 85.306761: bprint: walk_component: inode=(nil) dentry=0xee3c0240 neg:0 flags:200088 That was with this: trace_printk("inode=%p dentry=%p neg:%d\n", inode, path->dentry, d_is_negative(path->dentry)); err = -ENOENT; if (d_is_negative(path->dentry)) goto out_path_put; trace_printk("inode=%p dentry=%p neg:%d flags:%lx\n", inode, path->dentry, d_is_negative(path->dentry), (long)path->dentry->d_flags); -- Steve