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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 4CC24C76195 for ; Fri, 19 Jul 2019 04:17:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 26CDF2082F for ; Fri, 19 Jul 2019 04:17:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563509854; bh=wkAGBGsIOz7ocQoR+xQeCTnxMLX7lj5Q/aPZDGMTImU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=JD08STOJ3SIv7v1yxPS8wQh+O7XbjM5O6u0pj+62h9410S4JYoYbiWAGM/6nfTBRx JBrszPMP4X1Yxe0D94yt8wABpKcnS9Vcp8its+xjv5aCwx2IYHjEjwzEl4UyZ0vA+N PWAxH/B3DIlSA3ChfaS/wmsjXtoafYEndYHD5D98= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389566AbfGSERc (ORCPT ); Fri, 19 Jul 2019 00:17:32 -0400 Received: from mail.kernel.org ([198.145.29.99]:50512 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732631AbfGSEOV (ORCPT ); Fri, 19 Jul 2019 00:14:21 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 11FAC21873; Fri, 19 Jul 2019 04:14:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563509661; bh=wkAGBGsIOz7ocQoR+xQeCTnxMLX7lj5Q/aPZDGMTImU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2FKTdMgnKygiNhPdlK4RZBcGRMT6+62sRMSWPZxR2B5epCKRyWv9RlMylkc4eVwmZ jXfQEsW0iJNN6QOUMp7g3DrupxSEONuTY1/Ym08VXKejZHprVtMIUpBPFKCPjLwiDq foEcnhxVsFNFKKW++5LUj9vOjo/rA7xqt8FoEdY0= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Jean-Philippe Brucker , =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Michal Hocko , Andrew Morton , Linus Torvalds , Sasha Levin , linux-mm@kvack.org Subject: [PATCH AUTOSEL 4.9 44/45] mm/mmu_notifier: use hlist_add_head_rcu() Date: Fri, 19 Jul 2019 00:13:03 -0400 Message-Id: <20190719041304.18849-44-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190719041304.18849-1-sashal@kernel.org> References: <20190719041304.18849-1-sashal@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jean-Philippe Brucker [ 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