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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 41481C433FF for ; Fri, 2 Aug 2019 10:00:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 194AD2064A for ; Fri, 2 Aug 2019 10:00:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564740014; bh=cc+PpYXY8wQ9cF1G23aXSTEdh27NousCqZZ3bCOIbro=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=QJMa47Oboilem3LxLphvV/2FJyzyq+qgrC3f+38qUO3Dw/dXkftZNYlLfTaZ4rQBj Lf6dZEKZO0tEztza3V2Dt/iRJbB4XzfSEQMV3a4p1BHtmsyd8ZeFOkMewR115X2ljt znkrlL6SbrDlZxITTjEyGi93Mn2sAmkWL6AXZd/E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405389AbfHBJwx (ORCPT ); Fri, 2 Aug 2019 05:52:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:58472 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2406056AbfHBJwm (ORCPT ); Fri, 2 Aug 2019 05:52:42 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1F3B620665; Fri, 2 Aug 2019 09:52:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564739561; bh=cc+PpYXY8wQ9cF1G23aXSTEdh27NousCqZZ3bCOIbro=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=y87zscoWsUZRMjiuEuFUHQ9/4o7X80NTPotYrUs1zSsITlkKHfvRHO9g0CDW+X55Z DuFHrslkIyHbTTipP6p/O6QxDkXrCWZtsKmvRv0l3I+avXWJX7MmP5dIf1c8Eb76Nh UFKMSDTsV8NmBFO/HgiAc2GrJEMKk95W0wFfuenQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jean-Philippe Brucker , =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Michal Hocko , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 4.9 199/223] mm/mmu_notifier: use hlist_add_head_rcu() Date: Fri, 2 Aug 2019 11:37:04 +0200 Message-Id: <20190802092250.064816132@linuxfoundation.org> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190802092238.692035242@linuxfoundation.org> References: <20190802092238.692035242@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ Upstream commit 543bdb2d825fe2400d6e951f1786d92139a16931 ] Make mmu_notifier_register() safer by issuing a memory barrier before registering a new notifier. This fixes a theoretical bug on weakly ordered CPUs. For example, take this simplified use of notifiers by a driver: my_struct->mn.ops = &my_ops; /* (1) */ mmu_notifier_register(&my_struct->mn, mm) ... hlist_add_head(&mn->hlist, &mm->mmu_notifiers); /* (2) */ ... Once mmu_notifier_register() releases the mm locks, another thread can invalidate a range: mmu_notifier_invalidate_range() ... hlist_for_each_entry_rcu(mn, &mm->mmu_notifiers, hlist) { if (mn->ops->invalidate_range) The read side relies on the data dependency between mn and ops to ensure that the pointer is properly initialized. But the write side doesn't have any dependency between (1) and (2), so they could be reordered and the readers could dereference an invalid mn->ops. mmu_notifier_register() does take all the mm locks before adding to the hlist, but those have acquire semantics which isn't sufficient. By calling hlist_add_head_rcu() instead of hlist_add_head() we update the hlist using a store-release, ensuring that readers see prior initialization of my_struct. This situation is better illustated by litmus test MP+onceassign+derefonce. Link: http://lkml.kernel.org/r/20190502133532.24981-1-jean-philippe.brucker@arm.com Fixes: cddb8a5c14aa ("mmu-notifiers: core") Signed-off-by: Jean-Philippe Brucker Cc: Jérôme Glisse Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- 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 f4259e496f83..7a66e37efb4d 100644 --- a/mm/mmu_notifier.c +++ b/mm/mmu_notifier.c @@ -286,7 +286,7 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn, * thanks to mm_take_all_locks(). */ spin_lock(&mm->mmu_notifier_mm->lock); - hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list); + hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier_mm->list); spin_unlock(&mm->mmu_notifier_mm->lock); mm_drop_all_locks(mm); -- 2.20.1