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=ham 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 96BCDC32750 for ; Fri, 2 Aug 2019 09:35:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 71BA22184D for ; Fri, 2 Aug 2019 09:35:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564738527; bh=uHZHfjJtUWc+mrMGGjekpwtVMwWSmtYBS8YZx8R0QgM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=hELgwSEE4YGw1qq/y7nMvkYeUOQ+4NXXbWzm3jqsveGmFB3yuHWr1n51CtqzbCm5M zowZ8fZNdoKlo37qtYMYlG3gVQC7mVsdF8lqYy8W8CZHdR3Zdg8w+k/Nk/zYd76g6O mIoXXLHGBu0RPY12TBAd8MFEQzrJTt9eiF2u+mGU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390688AbfHBJfZ (ORCPT ); Fri, 2 Aug 2019 05:35:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:35796 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2403845AbfHBJfU (ORCPT ); Fri, 2 Aug 2019 05:35:20 -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 AF67721773; Fri, 2 Aug 2019 09:35:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564738520; bh=uHZHfjJtUWc+mrMGGjekpwtVMwWSmtYBS8YZx8R0QgM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RQq2LQcLn6zhYfq3TP1g5V3BNI+FkmLJ86IXuqq/WAJvjkuOfaL8ZW+0ZhtZX2pCT i3ujYVCglwJYqlKofJLdHCCVTvFVCw0Fl2HLBv7yzLvJMkUc1bCEAEN0wnweRipLW1 so+MsQ2FQSYBU7t50U9pI6rnEJlLred9WAtJyK0w= 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 4.4 136/158] mm/mmu_notifier: use hlist_add_head_rcu() Date: Fri, 2 Aug 2019 11:29:17 +0200 Message-Id: <20190802092230.781546358@linuxfoundation.org> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190802092203.671944552@linuxfoundation.org> References: <20190802092203.671944552@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 5fbdd367bbed..ad90b8f85223 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