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 X-Spam-Level: X-Spam-Status: No, score=-20.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38CEEC433DF for ; Fri, 16 Oct 2020 23:09:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DA11620874 for ; Fri, 16 Oct 2020 23:09:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="rClZn7/P" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406990AbgJPXJz (ORCPT ); Fri, 16 Oct 2020 19:09:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50260 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2407671AbgJPXJp (ORCPT ); Fri, 16 Oct 2020 19:09:45 -0400 Received: from mail-wr1-x442.google.com (mail-wr1-x442.google.com [IPv6:2a00:1450:4864:20::442]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ABE70C061755 for ; Fri, 16 Oct 2020 16:09:44 -0700 (PDT) Received: by mail-wr1-x442.google.com with SMTP id s9so4847654wro.8 for ; Fri, 16 Oct 2020 16:09:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=J4AQ8wqNpjVt1ykz0FMlQ/Hn0cAH4pxEjRmJmEVEXzM=; b=rClZn7/P2brEcbJ17hk3v5Ov20ONpnJc3N7mscK6TVtzEI4C2dZVcNCjb2UbK3GcrH KOrmC+GfSAgf5CBO5WNij6aH3a293buv1EwV41bQyMSXwzh3MJn0iVkBEv+G7SWWNczj vtzPCkqVAbbr0bjfD35ZzQpr1Lgn5CWWWEo3YXHFLlZ8tkf99ubo03jvazvBLhHOC1xP 8gQ+Xx3eR9NO0/YTyQOT7IdV6mTksrXqZTCaWg2l4hqnPa7E/QS3IEX9eLUnc7yluLWQ xj88YsUnFOCQpCiwuPuGMsh2AevEdExmakr+DPQ/A9NSXLpx5p+Kxfi/o7cfTQtApJEc NN4w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=J4AQ8wqNpjVt1ykz0FMlQ/Hn0cAH4pxEjRmJmEVEXzM=; b=YGKtQRkx/zqicM6sF3isrdzLrkPwCQqGsFt/dZZWZv+ID7e+gg1rv3m+Oozd59cSVU Lu8sopGuLoY1nUcg3GxDt0xQTkbxPD7gTn6xVQ47hl60ethD5d/3wKRPyke+z+zTJhXP 7qHAqtegU77kYbVdi2TEp0bcRcBNtRvD35I8ApHzZmm15WN4v01bzOBbaxkByhmXaO8I xbiif+w6NApgCxWe/4BKBwepMfk3vBiaVKZ9zg7d3jx4rCwQdnDwCKNOwEn6GpbLTteL m6n4WiFTrXWDlyXSbGmm2m2Uq+6eUMaaVQMWZM5q8krGyTgpkhyCGZ/20Vi9Fp6tZh93 houA== X-Gm-Message-State: AOAM530fhKueHOWAl9tH1s0a+PzNBoGncJw65Wc5AyDGgM/fvaO6DogB RSM3XQiB4NLZXjQbMGG4QGGDYQ== X-Google-Smtp-Source: ABdhPJzEacUrzZyN0193KfsbDyP+Nq2E/fuEoba3R3HJmfpoAO6isYjIW2vwr6uW3TdeSSNG7cYQgg== X-Received: by 2002:adf:e6c4:: with SMTP id y4mr6904873wrm.423.1602889783182; Fri, 16 Oct 2020 16:09:43 -0700 (PDT) Received: from localhost ([2a02:168:96c5:1:55ed:514f:6ad7:5bcc]) by smtp.gmail.com with ESMTPSA id q6sm4718202wma.0.2020.10.16.16.09.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Oct 2020 16:09:42 -0700 (PDT) From: Jann Horn To: Andrew Morton , linux-mm@kvack.org, Eric Biederman , Oleg Nesterov Cc: linux-kernel@vger.kernel.org, Will Deacon , Kees Cook , Ingo Molnar Subject: [RFC PATCH resend 4/6] mm, oom: Use mm_ref()/mm_unref() and avoid mmdrop_async() Date: Sat, 17 Oct 2020 01:09:13 +0200 Message-Id: <20201016230915.1972840-5-jannh@google.com> X-Mailer: git-send-email 2.29.0.rc1.297.gfa9743e501-goog In-Reply-To: <20201016230915.1972840-1-jannh@google.com> References: <20201016230915.1972840-1-jannh@google.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The OOM killer uses MMF_OOM_SKIP to avoid running on an mm that has started __mmput(); it only uses the mmgrab() reference to ensure that the mm_struct itself stays alive. This means that we don't need a full mmgrab() reference, which will keep the pgd (and potentially also some pmd pages) alive and can't be cleaned up from RCU callback context; we can use an mm_ref() reference instead. Signed-off-by: Jann Horn --- kernel/fork.c | 6 +----- mm/oom_kill.c | 2 +- 2 files changed, 2 insertions(+), 6 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index fcdd1ace79e4..59c119b03351 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -686,12 +686,8 @@ static inline void free_signal_struct(struct signal_st= ruct *sig) { taskstats_tgid_free(sig); sched_autogroup_exit(sig); - /* - * __mmdrop is not safe to call from softirq context on x86 due to - * pgd_dtor so postpone it to the async context - */ if (sig->oom_mm) - mmdrop_async(sig->oom_mm); + mm_unref(sig->oom_mm); kmem_cache_free(signal_cachep, sig); } =20 diff --git a/mm/oom_kill.c b/mm/oom_kill.c index e90f25d6385d..12967f54fbcf 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -704,7 +704,7 @@ static void mark_oom_victim(struct task_struct *tsk) =20 /* oom_mm is bound to the signal struct life time. */ if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) { - mmgrab(tsk->signal->oom_mm); + mm_ref(tsk->signal->oom_mm); set_bit(MMF_OOM_VICTIM, &mm->flags); } =20 --=20 2.29.0.rc1.297.gfa9743e501-goog