From patchwork Thu Jun 7 22:05:46 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 10453617 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 099EC60375 for ; Thu, 7 Jun 2018 22:05:52 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id ED2FF2995E for ; Thu, 7 Jun 2018 22:05:51 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id E18FB29967; Thu, 7 Jun 2018 22:05:51 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id BEB1E2995F for ; Thu, 7 Jun 2018 22:05:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751752AbeFGWFt (ORCPT ); Thu, 7 Jun 2018 18:05:49 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36888 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751231AbeFGWFs (ORCPT ); Thu, 7 Jun 2018 18:05:48 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.9.92]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 952F589B; Thu, 7 Jun 2018 22:05:47 +0000 (UTC) Date: Thu, 7 Jun 2018 15:05:46 -0700 From: Andrew Morton To: Tetsuo Handa , penguin-kernel@I-love.SAKURA.ne.jp, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, kirill.shutemov@linux.intel.com, mhocko@suse.com, riel@redhat.com, Matthew Wilcox Subject: Re: [PATCH] mm: Check for SIGKILL inside dup_mmap() loop. Message-Id: <20180607150546.1c7db21f70221008e14b8bb8@linux-foundation.org> In-Reply-To: <20180418193254.2db529eeca5d0dc5b82f6b3e@linux-foundation.org> References: <201804071938.CDE04681.SOFVQJFtMHOOLF@I-love.SAKURA.ne.jp> <20180418144401.7c9311079914803c9076d209@linux-foundation.org> <201804190154.w3J1sieH011800@www262.sakura.ne.jp> <20180418193254.2db529eeca5d0dc5b82f6b3e@linux-foundation.org> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Despite all the discussion, we're short on formal review/ack tags on this one. Here's what I have: From: Tetsuo Handa Subject: mm: check for SIGKILL inside dup_mmap() loop As a theoretical problem, dup_mmap() of an mm_struct with 60000+ vmas can loop while potentially allocating memory, with mm->mmap_sem held for write by current thread. This is bad if current thread was selected as an OOM victim, for current thread will continue allocations using memory reserves while OOM reaper is unable to reclaim memory. As an actually observable problem, it is not difficult to make OOM reaper unable to reclaim memory if the OOM victim is blocked at i_mmap_lock_write() in this loop. Unfortunately, since nobody can explain whether it is safe to use killable wait there, let's check for SIGKILL before trying to allocate memory. Even without an OOM event, there is no point with continuing the loop from the beginning if current thread is killed. I tested with debug printk(). This patch should be safe because we already fail if security_vm_enough_memory_mm() or kmem_cache_alloc(GFP_KERNEL) fails and exit_mmap() handles it. [ 417.030691] ***** Aborting dup_mmap() due to SIGKILL ***** [ 417.036129] ***** Aborting dup_mmap() due to SIGKILL ***** [ 417.044544] ***** Aborting dup_mmap() due to SIGKILL ***** [ 419.116445] ***** Aborting dup_mmap() due to SIGKILL ***** [ 419.118401] ***** Aborting exit_mmap() due to NULL mmap ***** [akpm@linux-foundation.org: add comment] Link: http://lkml.kernel.org/r/201804071938.CDE04681.SOFVQJFtMHOOLF@I-love.SAKURA.ne.jp Signed-off-by: Tetsuo Handa Cc: Alexander Viro Cc: Rik van Riel Cc: Michal Hocko Cc: Kirill A. Shutemov Cc: David Rientjes Signed-off-by: Andrew Morton Reviewed-by: Matthew Wilcox --- kernel/fork.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff -puN kernel/fork.c~mm-check-for-sigkill-inside-dup_mmap-loop kernel/fork.c --- a/kernel/fork.c~mm-check-for-sigkill-inside-dup_mmap-loop +++ a/kernel/fork.c @@ -440,6 +440,14 @@ static __latent_entropy int dup_mmap(str continue; } charge = 0; + /* + * Don't duplicate many vmas if we've been oom-killed (for + * example) + */ + if (fatal_signal_pending(current)) { + retval = -EINTR; + goto out; + } if (mpnt->vm_flags & VM_ACCOUNT) { unsigned long len = vma_pages(mpnt);