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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 721A7C433EF for ; Wed, 8 Dec 2021 09:02:06 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 07D696B0074; Wed, 8 Dec 2021 04:01:56 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 02CE96B0075; Wed, 8 Dec 2021 04:01:55 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E5E096B0078; Wed, 8 Dec 2021 04:01:55 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay029.a.hostedemail.com [64.99.140.29]) by kanga.kvack.org (Postfix) with ESMTP id D7CD16B0074 for ; Wed, 8 Dec 2021 04:01:55 -0500 (EST) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id AC9D760333 for ; Wed, 8 Dec 2021 09:01:45 +0000 (UTC) X-FDA: 78894034170.27.4380533 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf14.hostedemail.com (Postfix) with ESMTP id 32ED0600199F for ; Wed, 8 Dec 2021 09:01:45 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id F37CB212C3; Wed, 8 Dec 2021 09:01:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1638954104; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=SPcplUKbn+26/lhn9RIJqQ7lmPcyVCiNERjtv5vh+2s=; b=jrphflUAN+2NwFR/Y6VoUtqVOwgDqdWgXqyP3F2oRbbH7+BUvHm8o6Q2clTqs8pb9ER3yz 9HNpEwOHqe9CAbQARH8p3fGiyjEID5R8B3Wlps+HCRQfq+kGQSCPglQFp78HLFn26bxg82 Z/QoETq/OjMURAY7S+TW/thXN4aj+WY= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 8D7EAA3B91; Wed, 8 Dec 2021 09:01:43 +0000 (UTC) Date: Wed, 8 Dec 2021 10:01:43 +0100 From: Michal Hocko To: Andrew Morton Cc: Joel Savitz , linux-kernel@vger.kernel.org, Waiman Long , linux-mm@kvack.org, Nico Pache , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Darren Hart , Davidlohr Bueso , =?iso-8859-1?Q?Andr=E9?= Almeida Subject: Re: [PATCH] mm/oom_kill: wake futex waiters before annihilating victim shared mutex Message-ID: References: <20211207214902.772614-1-jsavitz@redhat.com> <20211207154759.3f3fe272349c77e0c4aca36f@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211207154759.3f3fe272349c77e0c4aca36f@linux-foundation.org> X-Stat-Signature: o1cu3kujrscsir6jewoccqaz6nwcjham Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=jrphflUA; spf=pass (imf14.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 32ED0600199F X-HE-Tag: 1638954105-671514 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 07-12-21 15:47:59, Andrew Morton wrote: > (cc's added) Extend CC to have all futex maintainers on board. > On Tue, 7 Dec 2021 16:49:02 -0500 Joel Savitz wrote: > > > In the case that two or more processes share a futex located within > > a shared mmaped region, such as a process that shares a lock between > > itself and a number of child processes, we have observed that when > > a process holding the lock is oom killed, at least one waiter is never > > alerted to this new development and simply continues to wait. > > Well dang. Is there any way of killing off that waiting process, or do > we have a resource leak here? > > > This is visible via pthreads by checking the __owner field of the > > pthread_mutex_t structure within a waiting process, perhaps with gdb. > > > > We identify reproduction of this issue by checking a waiting process of > > a test program and viewing the contents of the pthread_mutex_t, taking note > > of the value in the owner field, and then checking dmesg to see if the > > owner has already been killed. > > > > This issue can be tricky to reproduce, but with the modifications of > > this small patch, I have found it to be impossible to reproduce. There > > may be additional considerations that I have not taken into account in > > this patch and I welcome any comments and criticism. Why does OOM killer need a special handling. All the oom killer does is to send a fatal signal to the victim. Why is this any different from sending SIGKILL from the userspace? > > Co-developed-by: Nico Pache > > Signed-off-by: Nico Pache > > Signed-off-by: Joel Savitz > > --- > > mm/oom_kill.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index 1ddabefcfb5a..fa58bd10a0df 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -44,6 +44,7 @@ > > #include > > #include > > #include > > +#include > > > > #include > > #include "internal.h" > > @@ -890,6 +891,7 @@ static void __oom_kill_process(struct task_struct *victim, const char *message) > > * in order to prevent the OOM victim from depleting the memory > > * reserves from the user space under its control. > > */ > > + futex_exit_release(victim); > > do_send_sig_info(SIGKILL, SEND_SIG_PRIV, victim, PIDTYPE_TGID); > > mark_oom_victim(victim); > > pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB, UID:%u pgtables:%lukB oom_score_adj:%hd\n", > > @@ -930,6 +932,7 @@ static void __oom_kill_process(struct task_struct *victim, const char *message) > > */ > > if (unlikely(p->flags & PF_KTHREAD)) > > continue; > > + futex_exit_release(p); > > do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID); > > } > > rcu_read_unlock(); > > -- > > 2.33.1 -- Michal Hocko SUSE Labs