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 4D6BAC4332F for ; Fri, 22 Oct 2021 02:25:02 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CFFAF613A9 for ; Fri, 22 Oct 2021 02:25:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org CFFAF613A9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 3031A900003; Thu, 21 Oct 2021 22:25:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2B1EC900002; Thu, 21 Oct 2021 22:25:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1EFE3900003; Thu, 21 Oct 2021 22:25:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0020.hostedemail.com [216.40.44.20]) by kanga.kvack.org (Postfix) with ESMTP id 10B1B900002 for ; Thu, 21 Oct 2021 22:25:01 -0400 (EDT) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id A239D3017B for ; Fri, 22 Oct 2021 02:25:00 +0000 (UTC) X-FDA: 78722480760.17.2EC30B5 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf10.hostedemail.com (Postfix) with ESMTP id 634086001993 for ; Fri, 22 Oct 2021 02:24:55 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id A004360551; Fri, 22 Oct 2021 02:24:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1634869499; bh=ba3gyIn2Qaclz/r/YcqNfTvZdQP29SgCT1X+NCF/gLk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=xlKO7/DGTNQ44ucClRz9f14c2t0IN5jZj2/SBtx+IgXvkDCj3wXOXzOrF152/Y8n9 Mjvo3ezH0mryi0MeclaXi4j34fgfeoL7dbF0Dw7Gz2WfUZN9icZv26BHrjpylr5Fah 1tgSHLAr6MPLBpwFxtrSfdbznmzYtwXpFZ5w1SlE= Date: Thu, 21 Oct 2021 19:24:54 -0700 From: Andrew Morton To: Suren Baghdasaryan Cc: mhocko@kernel.org, mhocko@suse.com, rientjes@google.com, willy@infradead.org, hannes@cmpxchg.org, guro@fb.com, riel@surriel.com, minchan@kernel.org, christian@brauner.io, hch@infradead.org, oleg@redhat.com, david@redhat.com, jannh@google.com, shakeelb@google.com, luto@kernel.org, christian.brauner@ubuntu.com, fweimer@redhat.com, jengelh@inai.de, linux-api@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH 1/1] mm: prevent a race between process_mrelease and exit_mmap Message-Id: <20211021192454.72ada9b3d59460cc3c037d2c@linux-foundation.org> In-Reply-To: <20211022014658.263508-1-surenb@google.com> References: <20211022014658.263508-1-surenb@google.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 634086001993 X-Stat-Signature: modwunnkjuqnapk1casfh8tb93qnmabr Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b="xlKO7/DG"; dmarc=none; spf=pass (imf10.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-HE-Tag: 1634869495-431646 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 Thu, 21 Oct 2021 18:46:58 -0700 Suren Baghdasaryan wrote: > 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. Has the impact been quantified? And where's the added cost happening? The changes all look quite lightweight?