Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753919AbbGNVQW (ORCPT ); Tue, 14 Jul 2015 17:16:22 -0400 Received: from mail-ie0-f170.google.com ([209.85.223.170]:33797 "EHLO mail-ie0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753883AbbGNVQU (ORCPT ); Tue, 14 Jul 2015 17:16:20 -0400 Date: Tue, 14 Jul 2015 14:16:18 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Hillf Danton cc: Andrew Morton , Sergey Senozhatsky , Michal Hocko , linux-kernel , linux-mm@kvack.org Subject: RE: [patch v3 3/3] mm, oom: do not panic for oom kills triggered from sysrq In-Reply-To: <050601d0bae5$14647770$3d2d6650$@alibaba-inc.com> Message-ID: References: <02e601d0b9fd$d644ec50$82cec4f0$@alibaba-inc.com> <050601d0bae5$14647770$3d2d6650$@alibaba-inc.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1758 Lines: 46 On Fri, 10 Jul 2015, Hillf Danton wrote: > > I'm not sure I understand your point. > > > > There are two oom killer panics: when panic_on_oom is enabled and when the > > oom killer can't find an eligible process. > > > > The change to the panic_on_oom panic is dealt with in check_panic_on_oom() > > and the no eligible process panic is dealt with here. > > > > If the sysctl is disabled, and there are no eligible processes to kill, > > the change in behavior here is that we don't panic when triggered from > > sysrq. That's the change in the hunk above. > > > When no eligible processes is selected to kill, we are sure that we skip one > panic in check_panic_on_oom(), and we have no clear reason to panic again. > > But we can simply answer the caller that there is no page, and let her > decide what to do. > > So I prefer to fold the two panic into one. > > Hillf > > > > - if (p != (void *)-1UL) { > > > > + if (p && p != (void *)-1UL) { > > > > oom_kill_process(oc, p, points, totalpages, NULL, > > > > "Out of memory"); > > > > killed = 1; > I'm still not sure I understand your point, unfortunately. The new check: if (!p && oc->order != -1) { dump_header(oc, NULL, NULL); panic("Out of memory and no killable processes...\n"); } ensures we never panic when called from sysrq. This is done because userspace can easily race when there is a single eligible process to kill that exits or is otherwise killed and the sysrq+f ends up panicking the machine unexpectedly. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/