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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 F2BCCC432C2 for ; Tue, 24 Sep 2019 10:54:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9E9321655 for ; Tue, 24 Sep 2019 10:54:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569322440; bh=TKkEZXgQ6QrHyhUZpGQvpt1dC+CcQNzfSneNFogv0oA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=xOQgkEUdF2sPq282FvcsXS0u9LVwKP+5hrDyyd2sl3EkLod7YAJxrmjKGbFGz/Dsx 7Pk+TCbf7AWfr2C+lbzZFX19bjQ1bMsOUuSYlenO/Gio1jHOcxpbCePh+DTD0XMZQZ 7ekmRKmey0gzAcsIgp9S260sL3X5gDq7mS0EaAq8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2440768AbfIXKyA (ORCPT ); Tue, 24 Sep 2019 06:54:00 -0400 Received: from mx2.suse.de ([195.135.220.15]:33116 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2438809AbfIXKx7 (ORCPT ); Tue, 24 Sep 2019 06:53:59 -0400 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 D7807ACA0; Tue, 24 Sep 2019 10:53:56 +0000 (UTC) Date: Tue, 24 Sep 2019 12:53:55 +0200 From: Michal Hocko To: Andrew Morton Cc: Johannes Weiner , Vladimir Davydov , LKML , linux-mm@kvack.org, Andrey Ryabinin , Thomas Lindroth , Tetsuo Handa Subject: Re: [PATCH] memcg, kmem: do not fail __GFP_NOFAIL charges Message-ID: <20190924105355.GA28904@dhcp22.suse.cz> References: <31131c2d-a936-8bbf-e58d-a3baaa457340@gmail.com> <20190906125608.32129-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190906125608.32129-1-mhocko@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew, do you plan to send this patch to Linus as ell? On Fri 06-09-19 14:56:08, Michal Hocko wrote: > From: Michal Hocko > > Thomas has noticed the following NULL ptr dereference when using cgroup > v1 kmem limit: > BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 > PGD 0 > P4D 0 > Oops: 0000 [#1] PREEMPT SMP PTI > CPU: 3 PID: 16923 Comm: gtk-update-icon Not tainted 4.19.51 #42 > Hardware name: Gigabyte Technology Co., Ltd. Z97X-Gaming G1/Z97X-Gaming G1, BIOS F9 07/31/2015 > RIP: 0010:create_empty_buffers+0x24/0x100 > Code: cd 0f 1f 44 00 00 0f 1f 44 00 00 41 54 49 89 d4 ba 01 00 00 00 55 53 48 89 fb e8 97 fe ff ff 48 89 c5 48 89 c2 eb 03 48 89 ca <48> 8b 4a 08 4c 09 22 48 85 c9 75 f1 48 89 6a 08 48 8b 43 18 48 8d > RSP: 0018:ffff927ac1b37bf8 EFLAGS: 00010286 > RAX: 0000000000000000 RBX: fffff2d4429fd740 RCX: 0000000100097149 > RDX: 0000000000000000 RSI: 0000000000000082 RDI: ffff9075a99fbe00 > RBP: 0000000000000000 R08: fffff2d440949cc8 R09: 00000000000960c0 > R10: 0000000000000002 R11: 0000000000000000 R12: 0000000000000000 > R13: ffff907601f18360 R14: 0000000000002000 R15: 0000000000001000 > FS: 00007fb55b288bc0(0000) GS:ffff90761f8c0000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000008 CR3: 000000007aebc002 CR4: 00000000001606e0 > Call Trace: > create_page_buffers+0x4d/0x60 > __block_write_begin_int+0x8e/0x5a0 > ? ext4_inode_attach_jinode.part.82+0xb0/0xb0 > ? jbd2__journal_start+0xd7/0x1f0 > ext4_da_write_begin+0x112/0x3d0 > generic_perform_write+0xf1/0x1b0 > ? file_update_time+0x70/0x140 > __generic_file_write_iter+0x141/0x1a0 > ext4_file_write_iter+0xef/0x3b0 > __vfs_write+0x17e/0x1e0 > vfs_write+0xa5/0x1a0 > ksys_write+0x57/0xd0 > do_syscall_64+0x55/0x160 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > Tetsuo then noticed that this is because the __memcg_kmem_charge_memcg > fails __GFP_NOFAIL charge when the kmem limit is reached. This is a > wrong behavior because nofail allocations are not allowed to fail. > Normal charge path simply forces the charge even if that means to cross > the limit. Kmem accounting should be doing the same. > > Reported-by: Thomas Lindroth > Debugged-by: Tetsuo Handa > Cc: stable > Signed-off-by: Michal Hocko > --- > mm/memcontrol.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 9ec5e12486a7..e18108b2b786 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2821,6 +2821,16 @@ int __memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order, > > if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && > !page_counter_try_charge(&memcg->kmem, nr_pages, &counter)) { > + > + /* > + * Enforce __GFP_NOFAIL allocation because callers are not > + * prepared to see failures and likely do not have any failure > + * handling code. > + */ > + if (gfp & __GFP_NOFAIL) { > + page_counter_charge(&memcg->kmem, nr_pages); > + return 0; > + } > cancel_charge(memcg, nr_pages); > return -ENOMEM; > } > -- > 2.20.1 -- Michal Hocko SUSE Labs