From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A9696C432C1 for ; Tue, 24 Sep 2019 14:37:26 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6C47C2053B for ; Tue, 24 Sep 2019 14:37:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6C47C2053B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1E7E06B000E; Tue, 24 Sep 2019 10:37:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 19AC46B026A; Tue, 24 Sep 2019 10:37:26 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0AFDA6B026B; Tue, 24 Sep 2019 10:37:26 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id DC4886B000E for ; Tue, 24 Sep 2019 10:37:25 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 78CBD181AC9B4 for ; Tue, 24 Sep 2019 14:37:25 +0000 (UTC) X-FDA: 75970067250.24.ants96_7af92522a1b42 X-HE-Tag: ants96_7af92522a1b42 X-Filterd-Recvd-Size: 4595 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Tue, 24 Sep 2019 14:37:24 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id CC424AE22; Tue, 24 Sep 2019 14:37:23 +0000 (UTC) Date: Tue, 24 Sep 2019 16:37:23 +0200 From: Michal Hocko To: Baoquan He Cc: akpm@linux-foundation.org, ltj@kernel.org, inux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v3] memcg: Only record foreign writebacks with dirty pages when memcg is not disabled Message-ID: <20190924143723.GZ23050@dhcp22.suse.cz> References: <20190923083030.6442-1-bhe@redhat.com> <20190924111138.GA31919@MiWiFi-R3L-srv> <20190924141928.GD31919@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190924141928.GD31919@MiWiFi-R3L-srv> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 24-09-19 22:19:28, Baoquan He wrote: > In kdump kernel, memcg usually is disabled with 'cgroup_disable=memory' > for saving memory. Now kdump kernel will always panic when dump vmcore > to local disk: > > BUG: kernel NULL pointer dereference, address: 0000000000000ab8 > PGD 5fcab067 P4D 5fcab067 PUD 5ff73067 PMD 0 > Oops: 0000 [#1] SMP NOPTI > CPU: 0 PID: 598 Comm: makedumpfile Not tainted 5.3.0+ #26 > Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 10/02/2018 > RIP: 0010:mem_cgroup_track_foreign_dirty_slowpath+0x38/0x140 > Code: 55 48 8b 2d 6a bd 12 01 53 4c 8b 67 38 0f 1f 44 00 00 49 8b 06 48 89 e9 31 db be ff ff ff ff 48 8b 38 49 8d 84 24 d0 0a 00 00 <48> 39 78 e8 > 74 5a 48 8b 50 f8 48 39 ca 79 0e 44 8b 00 41 83 f8 01 > RSP: 0018:ffffbc9300817bd0 EFLAGS: 00010046 > RAX: 0000000000000ad0 RBX: 0000000000000000 RCX: 00000000fffba227 > RDX: fffffffffffffff8 RSI: 00000000ffffffff RDI: 0000000000000004 > RBP: 00000000fffba227 R08: 0000000000030340 R09: ffffbc9300817d10 > R10: 0000000000000000 R11: 0000000000001000 R12: 0000000000000000 > R13: ffff999c1fa2bcf0 R14: ffff999c1f7bcc78 R15: ffffe51fc177a8c0 > FS: 00007f84f14c2b80(0000) GS:ffff999c22200000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000ab8 CR3: 000000005f564000 CR4: 00000000003406b0 > Call Trace: > __set_page_dirty+0x52/0xc0 > iomap_set_page_dirty+0x50/0x90 > iomap_write_end+0x6e/0x270 > iomap_write_actor+0xce/0x170 > ? iomap_write_end+0x270/0x270 > iomap_apply+0xba/0x11e > ? iomap_write_end+0x270/0x270 > iomap_file_buffered_write+0x62/0x90 > ? iomap_write_end+0x270/0x270 > xfs_file_buffered_aio_write+0xca/0x320 [xfs] > new_sync_write+0x12d/0x1d0 > vfs_write+0xa5/0x1a0 > ksys_write+0x59/0xd0 > do_syscall_64+0x59/0x1e0 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > RIP: 0033:0x7f84f1093ab5 > > And this will corrupt the 1st kernel too with 'cgroup_disable=memory'. > > >From the trace and with debugging, it is pointing to commit 97b27821b485 > ("writeback, memcg: Implement foreign dirty flushing") which introduced > this regression. Disabling memcg causes the null pointer dereference at > uninitialized data in function mem_cgroup_track_foreign_dirty_slowpath(). > > Fix it by returning directly if memcg is disabled, but not trying to > record the foreign writebacks with dirty pages. > > Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing") > Signed-off-by: Baoquan He Looks good to me. This is essentially the same thing as if MEMCG was disabled completely AFAICS. Acked-by: Michal Hocko Thanks! > --- > v2->v3: > Move the checking into mem_cgroup_track_foreign_dirty() per Michal's > suggestions. > > include/linux/memcontrol.h | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index ad8f1a397ae4..0e0432dfac4d 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -1261,6 +1261,9 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct page *page, > static inline void mem_cgroup_track_foreign_dirty(struct page *page, > struct bdi_writeback *wb) > { > + if (mem_cgroup_disabled()) > + return; > + > if (unlikely(&page->mem_cgroup->css != wb->memcg_css)) > mem_cgroup_track_foreign_dirty_slowpath(page, wb); > } > -- > 2.17.2 -- Michal Hocko SUSE Labs