From patchwork Fri Jan 14 18:01:35 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nico Pache X-Patchwork-Id: 12713878 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 D7779C433EF for ; Fri, 14 Jan 2022 18:02:47 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0C7BF6B0071; Fri, 14 Jan 2022 13:02:47 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 051246B0073; Fri, 14 Jan 2022 13:02:46 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E0BA26B0074; Fri, 14 Jan 2022 13:02:46 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0173.hostedemail.com [216.40.44.173]) by kanga.kvack.org (Postfix) with ESMTP id CA5EE6B0071 for ; Fri, 14 Jan 2022 13:02:46 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 7F63E998B8 for ; Fri, 14 Jan 2022 18:02:46 +0000 (UTC) X-FDA: 79029663132.12.FB04B45 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf28.hostedemail.com (Postfix) with ESMTP id 4049AC000A for ; Fri, 14 Jan 2022 18:02:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1642183363; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=Zgi7kgPZpPYPdqiACX0LHJAeUyEaVTMb9kNv1vAmtfg=; b=V4qsQokc45L+z7/mrSpxFEf0vem3cRHFiNxH7rhWy5482WrvfCgHOJ/RZozg/wZkQs4LzE uzCPkF4DvBHo3bHV0B0sEHqhqZZhNc+FE6/VYZstWa5/eaclqubbA5NMwHUJLRfNs6gTVV TOfRD7yKv9j6iytALtIh+j1EGHQJJl8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-644-_8Ae0FRgO7-oBLoZmCQ1hw-1; Fri, 14 Jan 2022 13:02:40 -0500 X-MC-Unique: _8Ae0FRgO7-oBLoZmCQ1hw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D1F78101F000; Fri, 14 Jan 2022 18:02:38 +0000 (UTC) Received: from localhost.net (unknown [10.22.34.129]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4980E34941; Fri, 14 Jan 2022 18:02:23 +0000 (UTC) From: Nico Pache To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, jsavitz@redhat.com, mhocko@suse.com Cc: peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, dvhart@infradead.org, dave@stgolabs.net, andrealmeid@collabora.com, longman@redhat.com Subject: [PATCH v3] mm/oom: do not oom reap task with an unresolved robust futex Date: Fri, 14 Jan 2022 13:01:35 -0500 Message-Id: <20220114180135.83308-1-npache@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 4049AC000A X-Stat-Signature: hxx16afumkwukmysgt5ddoqbkwgqbk7m Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=V4qsQokc; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf28.hostedemail.com: domain of npache@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=npache@redhat.com X-HE-Tag: 1642183364-114188 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: 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 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. 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. As mentioned by Michal in his patchset introducing the oom reaper, commit aac4536355496 ("mm, oom: introduce oom reaper"), the purpose of the oom reaper is to try and free memory more quickly; however, In the case that a robust futex is being used, we want to avoid utilizing the concurrent oom reaper. This is due to a race that can occur between the SIGKILL handling the robust futex, and the oom reaper freeing the memory needed to maintain the robust list. In the case that the oom victim is utilizing a robust futex, and the SIGKILL has not yet handled the futex death, the tsk->robust_list should be non-NULL. This issue can be tricky to reproduce, but with the modifications of this patch, we have found it to be impossible to reproduce. Add a check for tsk->robust_list is non-NULL in wake_oom_reaper() to return early and prevent waking the oom reaper. Reproducer: https://gitlab.com/jsavitz/oom_futex_reproducer Co-developed-by: Joel Savitz Signed-off-by: Joel Savitz Signed-off-by: Nico Pache --- mm/oom_kill.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 1ddabefcfb5a..3cdaac9c7de5 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -667,6 +667,21 @@ static void wake_oom_reaper(struct task_struct *tsk) if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags)) return; +#ifdef CONFIG_FUTEX + /* + * If the ooming task's SIGKILL has not finished handling the + * robust futex it is not correct to reap the mm concurrently. + * Do not wake the oom reaper when the task still contains a + * robust list. + */ + if (tsk->robust_list) + return; +#ifdef CONFIG_COMPAT + if (tsk->compat_robust_list) + return; +#endif +#endif + get_task_struct(tsk); spin_lock(&oom_reaper_lock);