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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1CC6C433F5 for ; Mon, 1 Nov 2021 18:24:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AAEEE61058 for ; Mon, 1 Nov 2021 18:24:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231812AbhKAS0o (ORCPT ); Mon, 1 Nov 2021 14:26:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:45248 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231841AbhKAS0m (ORCPT ); Mon, 1 Nov 2021 14:26:42 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id D65E860F45; Mon, 1 Nov 2021 18:24:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1635791048; bh=MJ7elyrZaRtE6DNqjqkeW+62pRRohQL7pYAqmMGhk6s=; h=Date:From:To:Subject:From; b=pkUOnXO+6Png9wfvQi6VZJyWvvdU/Wtd34ONM3ZY7XsXRvkc04O9rhAca84I54CKn d8ygtLYoGMKkzWN1u6bIIzZCjogdNqugop4yCRuDx7PudOlYr+/D5yabV94kZ4xKSD VilZo+dOLNy81X8gvoC8YXk/JW9FN4OAF28vANEk= Date: Mon, 01 Nov 2021 11:24:07 -0700 From: akpm@linux-foundation.org To: christian.brauner@ubuntu.com, christian@brauner.io, david@redhat.com, fweimer@redhat.com, guro@fb.com, hannes@cmpxchg.org, hch@infradead.org, jannh@google.com, jengelh@inai.de, luto@kernel.org, mhocko@suse.com, minchan@kernel.org, mm-commits@vger.kernel.org, oleg@redhat.com, riel@surriel.com, rientjes@google.com, shakeelb@google.com, surenb@google.com, willy@infradead.org Subject: [merged] mm-prevent-a-race-between-process_mrelease-and-exit_mmap.patch removed from -mm tree Message-ID: <20211101182407.MuKIs0i14%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: mm/oom_kill.c: prevent a race between process_mrelease and exit_mmap has been removed from the -mm tree. Its filename was mm-prevent-a-race-between-process_mrelease-and-exit_mmap.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Suren Baghdasaryan Subject: mm/oom_kill.c: prevent a race between process_mrelease and exit_mmap Race between process_mrelease and exit_mmap, where free_pgtables is called while __oom_reap_task_mm is in progress, leads to kernel crash during pte_offset_map_lock call. oom-reaper avoids this race by setting MMF_OOM_VICTIM flag and causing exit_mmap to take and release mmap_write_lock, blocking it until oom-reaper releases mmap_read_lock. Reusing MMF_OOM_VICTIM for process_mrelease would be the simplest way to fix this race, however that would be considered a hack. Fix this race by elevating mm->mm_users and preventing exit_mmap from executing until process_mrelease is finished. Patch slightly refactors the code to adapt for a possible mmget_not_zero failure. This fix has considerable negative impact on process_mrelease performance and will likely need later optimization. Link: https://lkml.kernel.org/r/20211022014658.263508-1-surenb@google.com Fixes: 884a7e5964e0 ("mm: introduce process_mrelease system call") Signed-off-by: Suren Baghdasaryan Acked-by: Michal Hocko Cc: David Rientjes Cc: Matthew Wilcox (Oracle) Cc: Johannes Weiner Cc: Roman Gushchin Cc: Rik van Riel Cc: Minchan Kim Cc: Christian Brauner Cc: Christoph Hellwig Cc: Oleg Nesterov Cc: David Hildenbrand Cc: Jann Horn Cc: Shakeel Butt Cc: Andy Lutomirski Cc: Christian Brauner Cc: Florian Weimer Cc: Jan Engelhardt Signed-off-by: Andrew Morton --- mm/oom_kill.c | 23 ++++++++++++----------- 1 file changed, 12 insertions(+), 11 deletions(-) --- a/mm/oom_kill.c~mm-prevent-a-race-between-process_mrelease-and-exit_mmap +++ a/mm/oom_kill.c @@ -1150,7 +1150,7 @@ SYSCALL_DEFINE2(process_mrelease, int, p struct task_struct *task; struct task_struct *p; unsigned int f_flags; - bool reap = true; + bool reap = false; struct pid *pid; long ret = 0; @@ -1177,15 +1177,15 @@ SYSCALL_DEFINE2(process_mrelease, int, p goto put_task; } - mm = p->mm; - mmgrab(mm); - - /* If the work has been done already, just exit with success */ - if (test_bit(MMF_OOM_SKIP, &mm->flags)) - reap = false; - else if (!task_will_free_mem(p)) { - reap = false; - ret = -EINVAL; + if (mmget_not_zero(p->mm)) { + mm = p->mm; + if (task_will_free_mem(p)) + reap = true; + else { + /* Error only if the work has not been done already */ + if (!test_bit(MMF_OOM_SKIP, &mm->flags)) + ret = -EINVAL; + } } task_unlock(p); @@ -1201,7 +1201,8 @@ SYSCALL_DEFINE2(process_mrelease, int, p mmap_read_unlock(mm); drop_mm: - mmdrop(mm); + if (mm) + mmput(mm); put_task: put_task_struct(task); put_pid: _ Patches currently in -mm which might be from surenb@google.com are