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=-11.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 944EDC7618B for ; Thu, 25 Jul 2019 16:00:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 697262238C for ; Thu, 25 Jul 2019 16:00:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="BCgUAiiO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389784AbfGYQAo (ORCPT ); Thu, 25 Jul 2019 12:00:44 -0400 Received: from terminus.zytor.com ([198.137.202.136]:48059 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387874AbfGYQAn (ORCPT ); Thu, 25 Jul 2019 12:00:43 -0400 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id x6PG0Uue1070667 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Thu, 25 Jul 2019 09:00:30 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 terminus.zytor.com x6PG0Uue1070667 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2019071901; t=1564070431; bh=7XiOeA/D+HawhTDttdbmLI0yx6Nrxaq+KSSWvCxRWsI=; h=Date:From:Cc:Reply-To:In-Reply-To:References:To:Subject:From; b=BCgUAiiOFaDyryfeRzBoERMpc9En7sTFhMxa7RG4713YChFFbnfYb3SBHEV7QYRe/ UCWTq8ao7Ni/FPyFjIR1hoR3Pl5NnIQG23ENT+JxgyNuyDq8FIsUCEgU0kVRLtMt4K rnGvQdTCCgb+2VcsuNcfnyCgz8IYllqW5rlSENAAg9NNnaA0DhafBY1KrZS3CW4d2+ z3+Dgw+wQNxe7cuxSy8EX/uYNZChiBhH9Ie2/3l11e2aHYEvVm7UdCzbZJw4oUBsKr 4JBimxHL8GfBONAWT0ZJDR+Y9iN9QalolouwHPl+jFSg4wyeqroP5GuiI8jJ8QeL7/ ikPpgl6e3pe2w== Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id x6PG0TqZ1070661; Thu, 25 Jul 2019 09:00:29 -0700 Date: Thu, 25 Jul 2019 09:00:29 -0700 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Jan Stancek Message-ID: Cc: longman@redhat.com, linux-kernel@vger.kernel.org, mingo@kernel.org, hpa@zytor.com, will@kernel.org, peterz@infradead.org, jstancek@redhat.com, tglx@linutronix.de, torvalds@linux-foundation.org Reply-To: torvalds@linux-foundation.org, tglx@linutronix.de, jstancek@redhat.com, peterz@infradead.org, will@kernel.org, hpa@zytor.com, mingo@kernel.org, linux-kernel@vger.kernel.org, longman@redhat.com In-Reply-To: <50b8914e20d1d62bb2dee42d342836c2c16ebee7.1563438048.git.jstancek@redhat.com> References: <50b8914e20d1d62bb2dee42d342836c2c16ebee7.1563438048.git.jstancek@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/core] locking/rwsem: Add missing ACQUIRE to read_slowpath exit when queue is empty Git-Commit-ID: e1b98fa316648420d0434d9ff5b92ad6609ba6c3 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: e1b98fa316648420d0434d9ff5b92ad6609ba6c3 Gitweb: https://git.kernel.org/tip/e1b98fa316648420d0434d9ff5b92ad6609ba6c3 Author: Jan Stancek AuthorDate: Thu, 18 Jul 2019 10:51:25 +0200 Committer: Ingo Molnar CommitDate: Thu, 25 Jul 2019 15:39:23 +0200 locking/rwsem: Add missing ACQUIRE to read_slowpath exit when queue is empty LTP mtest06 has been observed to occasionally hit "still mapped when deleted" and following BUG_ON on arm64. The extra mapcount originated from pagefault handler, which handled pagefault for vma that has already been detached. vma is detached under mmap_sem write lock by detach_vmas_to_be_unmapped(), which also invalidates vmacache. When the pagefault handler (under mmap_sem read lock) calls find_vma(), vmacache_valid() wrongly reports vmacache as valid. After rwsem down_read() returns via 'queue empty' path (as of v5.2), it does so without an ACQUIRE on sem->count: down_read() __down_read() rwsem_down_read_failed() __rwsem_down_read_failed_common() raw_spin_lock_irq(&sem->wait_lock); if (list_empty(&sem->wait_list)) { if (atomic_long_read(&sem->count) >= 0) { raw_spin_unlock_irq(&sem->wait_lock); return sem; The problem can be reproduced by running LTP mtest06 in a loop and building the kernel (-j $NCPUS) in parallel. It does reproduces since v4.20 on arm64 HPE Apollo 70 (224 CPUs, 256GB RAM, 2 nodes). It triggers reliably in about an hour. The patched kernel ran fine for 10+ hours. Signed-off-by: Jan Stancek Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Will Deacon Acked-by: Waiman Long Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dbueso@suse.de Fixes: 4b486b535c33 ("locking/rwsem: Exit read lock slowpath if queue empty & no writer") Link: https://lkml.kernel.org/r/50b8914e20d1d62bb2dee42d342836c2c16ebee7.1563438048.git.jstancek@redhat.com Signed-off-by: Ingo Molnar --- kernel/locking/rwsem.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index bc91aacaab58..d3ce7c6c42a6 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -1036,6 +1036,8 @@ queue: */ if (adjustment && !(atomic_long_read(&sem->count) & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) { + /* Provide lock ACQUIRE */ + smp_acquire__after_ctrl_dep(); raw_spin_unlock_irq(&sem->wait_lock); rwsem_set_reader_owned(sem); lockevent_inc(rwsem_rlock_fast);