Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932091AbbBXSWw (ORCPT ); Tue, 24 Feb 2015 13:22:52 -0500 Received: from cantor2.suse.de ([195.135.220.15]:52747 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753420AbbBXSWv (ORCPT ); Tue, 24 Feb 2015 13:22:51 -0500 Date: Tue, 24 Feb 2015 19:22:50 +0100 From: Michal Hocko To: Andrew Morton Cc: David Rientjes , Johannes Weiner , "\\\"Rafael J. Wysocki\\\"" , Tetsuo Handa , linux-mm@kvack.org, LKML Subject: Re: [PATCH] mm, oom: do not fail __GFP_NOFAIL allocation if oom killer is disbaled Message-ID: <20150224182250.GE14939@dhcp22.suse.cz> References: <1424801964-1602-1-git-send-email-mhocko@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1424801964-1602-1-git-send-email-mhocko@suse.cz> 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 Content-Length: 3117 Lines: 83 On Tue 24-02-15 19:19:24, Michal Hocko wrote: > Tetsuo Handa has pointed out that __GFP_NOFAIL allocations might fail > after OOM killer is disabled if the allocation is performed by a > kernel thread. This behavior was introduced from the very beginning by > 7f33d49a2ed5 (mm, PM/Freezer: Disable OOM killer when tasks are frozen). > This means that the basic contract for the allocation request is broken > and the context requesting such an allocation might blow up unexpectedly. > > There are basically two ways forward. > 1) move oom_killer_disable after kernel threads are frozen. This has a > risk that the OOM victim wouldn't be able to finish because it would > depend on an already frozen kernel thread. This would be really > tricky to debug. > 2) do not fail GFP_NOFAIL allocation no matter what and risk a potential > Freezable kernel threads will loop and fail the suspend. Incidental > allocations after kernel threads are frozen will at least dump a > warning - if we are lucky and the serial console is still active of > course... > > This patch implements the later option because it is safer. We would see > warnings rather than allocation failures for the kernel threads which > would blow up otherwise and have a higher chances to identify > __GFP_NOFAIL users from deeper pm code. > > Signed-off-by: Michal Hocko > --- > > We haven't seen any bug reports Ups, forgot to save the file before sending. The full text is: " We haven't seen any bug reports since 2009 so I haven't marked the patch for stable. I have no problem to backport it to stable trees though if people think it is a good precaution. " > > mm/oom_kill.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 642f38cb175a..ea8b443cd871 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -772,6 +772,10 @@ out: > schedule_timeout_killable(1); > } > > +static DEFINE_RATELIMIT_STATE(oom_disabled_rs, > + DEFAULT_RATELIMIT_INTERVAL, > + DEFAULT_RATELIMIT_BURST); > + > /** > * out_of_memory - tries to invoke OOM killer. > * @zonelist: zonelist pointer > @@ -792,6 +796,10 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, > if (!oom_killer_disabled) { > __out_of_memory(zonelist, gfp_mask, order, nodemask, force_kill); > ret = true; > + } else if (gfp_mask & __GFP_NOFAIL) { > + if (__ratelimit(&oom_disabled_rs)) > + WARN(1, "Unable to make forward progress for __GFP_NOFAIL because OOM killer is disbaled\n"); > + ret = true; > } > up_read(&oom_sem); > > -- > 2.1.4 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Michal Hocko SUSE Labs -- 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/