From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751983AbdCSOFG (ORCPT ); Sun, 19 Mar 2017 10:05:06 -0400 Received: from mx2.suse.de ([195.135.220.15]:43139 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751877AbdCSOEz (ORCPT ); Sun, 19 Mar 2017 10:04:55 -0400 Date: Sun, 19 Mar 2017 10:04:47 -0400 From: Michal Hocko To: Linus Torvalds Cc: Tim Chen , "Huang, Ying" , Andrew Morton , linux-mm , Linux Kernel Mailing List Subject: Re: kernel BUG at mm/swap_slots.c:270 Message-ID: <20170319140447.GA12414@dhcp22.suse.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat 18-03-17 09:57:18, Linus Torvalds wrote: > Tim at al, > I got this on my desktop at shutdown: > > ------------[ cut here ]------------ > kernel BUG at mm/swap_slots.c:270! > invalid opcode: 0000 [#1] SMP > CPU: 5 PID: 1745 Comm: (sd-pam) Not tainted 4.11.0-rc1-00243-g24c534bb161b #1 > Hardware name: System manufacturer System Product Name/Z170-K, BIOS > 1803 05/06/2016 > RIP: 0010:free_swap_slot+0xba/0xd0 > Call Trace: > swap_free+0x36/0x40 > do_swap_page+0x360/0x6d0 > __handle_mm_fault+0x880/0x1080 > handle_mm_fault+0xd0/0x240 > __do_page_fault+0x232/0x4d0 > do_page_fault+0x20/0x70 > page_fault+0x22/0x30 > ---[ end trace aefc9ede53e0ab21 ]--- > > so there seems to be something screwy in the new swap_slots code. I am travelling (LSFMM) so I didn't get to look at this more thoroughly but it seems like a race because enable_swap_slots_cache is called at the very end of the swapon and we could have already created a swap entry for a page by that time I guess. > Any ideas? I'm not finding other reports of this, but I'm also not > seeing why it should BUG_ON(). The "use_swap_slot_cache" thing very > much checks whether swap_slot_cache_initialized has been set, so the > BUG_ON() just seems like garbage. But please take a look. I guess you are right. I cannot speak of the original intention but it seems Tim wanted to be careful to not see unexpected swap entry when the swap wasn't initialized yet. I would just drop the BUG_ON and bail out when the slot cache hasn't been initialized yet. -- Michal Hocko SUSE Labs