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=-5.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 6B225ECE563 for ; Mon, 17 Sep 2018 22:51:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C6BA2088F for ; Mon, 17 Sep 2018 22:51:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2C6BA2088F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729143AbeIREUx (ORCPT ); Tue, 18 Sep 2018 00:20:53 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:45026 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727086AbeIREUx (ORCPT ); Tue, 18 Sep 2018 00:20:53 -0400 Received: from localhost (li1825-44.members.linode.com [172.104.248.44]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 12DE6CAE; Mon, 17 Sep 2018 22:51:24 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Prateek Sood , "Peter Zijlstra (Intel)" , Linus Torvalds , Thomas Gleixner , sramana@codeaurora.org, Ingo Molnar , Amit Pundir Subject: [PATCH 4.4 12/56] locking/osq_lock: Fix osq_lock queue corruption Date: Tue, 18 Sep 2018 00:41:45 +0200 Message-Id: <20180917213828.470483080@linuxfoundation.org> X-Mailer: git-send-email 2.19.0 In-Reply-To: <20180917213827.913122591@linuxfoundation.org> References: <20180917213827.913122591@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review 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 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Prateek Sood commit 50972fe78f24f1cd0b9d7bbf1f87d2be9e4f412e upstream. Fix ordering of link creation between node->prev and prev->next in osq_lock(). A case in which the status of optimistic spin queue is CPU6->CPU2 in which CPU6 has acquired the lock. tail v ,-. <- ,-. |6| |2| `-' -> `-' At this point if CPU0 comes in to acquire osq_lock, it will update the tail count. CPU2 CPU0 ---------------------------------- tail v ,-. <- ,-. ,-. |6| |2| |0| `-' -> `-' `-' After tail count update if CPU2 starts to unqueue itself from optimistic spin queue, it will find an updated tail count with CPU0 and update CPU2 node->next to NULL in osq_wait_next(). unqueue-A tail v ,-. <- ,-. ,-. |6| |2| |0| `-' `-' `-' unqueue-B ->tail != curr && !node->next If reordering of following stores happen then prev->next where prev being CPU2 would be updated to point to CPU0 node: tail v ,-. <- ,-. ,-. |6| |2| |0| `-' `-' -> `-' osq_wait_next() node->next <- 0 xchg(node->next, NULL) tail v ,-. <- ,-. ,-. |6| |2| |0| `-' `-' `-' unqueue-C At this point if next instruction WRITE_ONCE(next->prev, prev); in CPU2 path is committed before the update of CPU0 node->prev = prev then CPU0 node->prev will point to CPU6 node. tail v----------. v ,-. <- ,-. ,-. |6| |2| |0| `-' `-' `-' `----------^ At this point if CPU0 path's node->prev = prev is committed resulting in change of CPU0 prev back to CPU2 node. CPU2 node->next is NULL currently, tail v ,-. <- ,-. <- ,-. |6| |2| |0| `-' `-' `-' `----------^ so if CPU0 gets into unqueue path of osq_lock it will keep spinning in infinite loop as condition prev->next == node will never be true. Signed-off-by: Prateek Sood [ Added pictures, rewrote comments. ] Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: sramana@codeaurora.org Link: http://lkml.kernel.org/r/1500040076-27626-1-git-send-email-prsood@codeaurora.org Signed-off-by: Ingo Molnar Signed-off-by: Amit Pundir Signed-off-by: Greg Kroah-Hartman --- kernel/locking/osq_lock.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -104,6 +104,19 @@ bool osq_lock(struct optimistic_spin_que prev = decode_cpu(old); node->prev = prev; + + /* + * osq_lock() unqueue + * + * node->prev = prev osq_wait_next() + * WMB MB + * prev->next = node next->prev = prev // unqueue-C + * + * Here 'node->prev' and 'next->prev' are the same variable and we need + * to ensure these stores happen in-order to avoid corrupting the list. + */ + smp_wmb(); + WRITE_ONCE(prev->next, node); /*