Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759276AbcLWIdl (ORCPT ); Fri, 23 Dec 2016 03:33:41 -0500 Received: from gum.cmpxchg.org ([85.214.110.215]:54078 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758391AbcLWIdj (ORCPT ); Fri, 23 Dec 2016 03:33:39 -0500 Date: Fri, 23 Dec 2016 03:33:29 -0500 From: Johannes Weiner To: Hugh Dickins Cc: Linus Torvalds , Dave Chinner , Chris Leech , Linux Kernel Mailing List , Lee Duncan , open-iscsi@googlegroups.com, Linux SCSI List , linux-block@vger.kernel.org, Christoph Hellwig Subject: Re: [4.10, panic, regression] iscsi: null pointer deref at iscsi_tcp_segment_done+0x20d/0x2e0 Message-ID: <20161223083329.GA13952@cmpxchg.org> References: <20161214222411.GH4326@dastard> <20161214222953.GI4326@dastard> <20161216185906.t2wmrr6wqjdsrduw@straylight.hirudinean.org> <20161221221638.GD4758@dastard> <20161222001303.nvrtm22szn3hgxar@straylight.hirudinean.org> <20161222051322.GF4758@dastard> <20161223073241.GA13584@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161223073241.GA13584@cmpxchg.org> User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2576 Lines: 48 On Fri, Dec 23, 2016 at 02:32:41AM -0500, Johannes Weiner wrote: > On Thu, Dec 22, 2016 at 12:22:27PM -0800, Hugh Dickins wrote: > > On Wed, 21 Dec 2016, Linus Torvalds wrote: > > > On Wed, Dec 21, 2016 at 9:13 PM, Dave Chinner wrote: > > > > I unmounted the fs, mkfs'd it again, ran the > > > > workload again and about a minute in this fired: > > > > > > > > [628867.607417] ------------[ cut here ]------------ > > > > [628867.608603] WARNING: CPU: 2 PID: 16925 at mm/workingset.c:461 shadow_lru_isolate+0x171/0x220 > > > > > > Well, part of the changes during the merge window were the shadow > > > entry tracking changes that came in through Andrew's tree. Adding > > > Johannes Weiner to the participants. > > > > > > > Now, this workload does not touch the page cache at all - it's > > > > entirely an XFS metadata workload, so it should not really be > > > > affecting the working set code. > > > > > > Well, I suspect that anything that creates memory pressure will end up > > > triggering the working set code, so .. > > > > > > That said, obviously memory corruption could be involved and result in > > > random issues too, but I wouldn't really expect that in this code. > > > > > > It would probably be really useful to get more data points - is the > > > problem reliably in this area, or is it going to be random and all > > > over the place. > > > > Data point: kswapd got WARNING on mm/workingset.c:457 in shadow_lru_isolate, > > soon followed by NULL pointer deref in list_lru_isolate, one time when > > I tried out Sunday's git tree. Not seen since, I haven't had time to > > investigate, just set it aside as something to worry about if it happens > > again. But it looks like shadow_lru_isolate() has issues beyond Dave's > > case (I've no XFS and no iscsi), suspect unrelated to his other problems. > > This seems consistent with what Dave observed: we encounter regular > pages in radix tree nodes on the shadow LRU that should only contain > nodes full of exceptional shadow entries. It could be an issue in the > new slot replacement code and the node tracking callback. Both encounters seem to indicate use-after-free. Dave's node didn't warn about an unexpected node->count / node->exceptional state, but had entries that were inconsistent with that. Hugh got the counter warning but crashed on a list_head that's not NULLed in a live node. workingset_update_node() should be called on page cache radix tree leaf nodes that go empty. I must be missing an update_node callback where a leaf node gets freed somewhere.