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=-12.8 required=3.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED,DKIM_INVALID,DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 B82FBC2BB4D for ; Tue, 1 Sep 2020 00:07:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9681B2100A for ; Tue, 1 Sep 2020 00:07:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=google.com header.i=@google.com header.b="Rp5RQjtH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726204AbgIAACe (ORCPT ); Mon, 31 Aug 2020 20:02:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52236 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726020AbgIAACe (ORCPT ); Mon, 31 Aug 2020 20:02:34 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A35DBC061573 for ; Mon, 31 Aug 2020 17:02:33 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id r1so11156761ybg.4 for ; Mon, 31 Aug 2020 17:02:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:message-id:mime-version:subject:from:to:cc; bh=/WK1I/ZsCqLXTjRuojbNjOezx7X+DvJD8ltypu8xs/g=; b=Rp5RQjtHdrOV9oOAdw+rlYP2b8FmTtHIgndUhzBsN6m2ht3rZ2dwnn8NuxI3w4UGT8 0J1LvrZkq4Lbr+l2dtcWKk+8RLUmXANtSDp10Uj9+GdaIMrkQu8TnpXfaQgWMcg93dej MIqACyfGvzUbrr5quNyAz+OwT49UB7EXJMfC91936uBlOeeDzjZkjTxvE7fXXhyhYhcX liBOmUqrs7fmCKcXilVo1NsHB6vvjsU2Kuy60NsXLe4saEIomU1vLqMoDK9cdIor/P0M iuTlHQW0c8U+yeM0rjV0VZ0otUkH4w/kl/1e/P8iES0nrVbuhU3CW1EEwdMGB2btJGoI gSug== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=/WK1I/ZsCqLXTjRuojbNjOezx7X+DvJD8ltypu8xs/g=; b=f3+oKEfwoZyKoPMm/CSgVypywVXuYowNgVaGayifsh90u4iq5kJFRO6bSC0t5ts315 0dUNqch70UlPgUJ40cdykye0abXjFyZwESgPq0qe9CL9ByDPqsyvHZG/BprMF9L9NJze hZjgJrrdxep/WwNDAn0dc+lYUmc0EEYu8An2Ctt3BZf1DMYJdiU7JMAL1vxlnMns9G98 O8l2bzKMxmyMHFJavytsFaImjSbLSVX6Apz/bhjMZQJ2sHc4miuXHbe9ZJvn6yABDvq6 r73YQNpTohzt+auJ24bs2G5xfHZr6yTcMM61MomB9WlnzIHE9JAXjioAyXHu5aX5i8iy IsPA== X-Gm-Message-State: AOAM533kL1phurHtiuTRIZIbLBqQAXT4EoLZTuKOB4RiQweQ/1qhTxjb f+KiDIeJvdB8oSyXMY1dMexa1AgWjQ== X-Google-Smtp-Source: ABdhPJwa8OHde2lQYnBK4sl7X9zvZNhHYLqhFJDFsng0d53MBPOB6RRRkl9jFfyBnOl/wZCGnBHzMaDZTg== X-Received: from jannh2.zrh.corp.google.com ([2a00:79e0:1b:201:1a60:24ff:fea6:bf44]) (user=jannh job=sendgmr) by 2002:a25:40cb:: with SMTP id n194mr6162269yba.7.1598918552892; Mon, 31 Aug 2020 17:02:32 -0700 (PDT) Date: Tue, 1 Sep 2020 02:01:43 +0200 Message-Id: <20200901000143.207585-1-jannh@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.28.0.402.g5ffc5be6b7-goog Subject: [PATCH] mm/mmu_notifier: Fix mmget() assert in __mmu_interval_notifier_insert From: Jann Horn To: Andrew Morton Cc: linux-mm@kvack.org, Jason Gunthorpe , John Hubbard , Christoph Hellwig , linux-kernel@vger.kernel.org, "=?UTF-8?q?Christian=20K=C3=B6nig?=" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The comment talks about having to hold mmget() (which means mm_users), but the actual check is on mm_count (which would be mmgrab()). Given that MMU notifiers are torn down in mmput() -> __mmput() -> exit_mmap() -> mmu_notifier_release(), I believe that the comment is correct and the check should be on mm->mm_users. Fix it up accordingly. Fixes: 99cb252f5e68 ("mm/mmu_notifier: add an interval tree notifier") Signed-off-by: Jann Horn --- Can someone please double-check this? I'm like 90% sure that I fixed this the right way around, but it'd be good if someone more familiar with mmu notifiers could confirm. mm/mmu_notifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c index 4fc918163dd3..5654dd19addc 100644 --- a/mm/mmu_notifier.c +++ b/mm/mmu_notifier.c @@ -913,7 +913,7 @@ static int __mmu_interval_notifier_insert( return -EOVERFLOW; /* Must call with a mmget() held */ - if (WARN_ON(atomic_read(&mm->mm_count) <= 0)) + if (WARN_ON(atomic_read(&mm->mm_users) <= 0)) return -EINVAL; /* pairs with mmdrop in mmu_interval_notifier_remove() */ base-commit: 15bc20c6af4ceee97a1f90b43c0e386643c071b4 -- 2.28.0.402.g5ffc5be6b7-goog