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 911CEC3A5A6 for ; Mon, 26 Aug 2019 14:31:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 687B8217F5 for ; Mon, 26 Aug 2019 14:31:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566829887; bh=S0V5XzeUw6fLtK+Xw7uttsjbYD3Xydm6LhgGRawrGX0=; h=From:To:Cc:Subject:Date:List-ID:From; b=e6CK5k0un+pdX7Q0wnLZu/wD8QAM0Rn87nF3kBtYDGpNpAOuHtgP+F4IXAfBe2FQa 2MDcEdrhluJUgm2B5EwoETYWkzfXpJIoCb555GjP1IrGNR2inI1jiD+8fmdV4sHBpV cpbwYTRx4VTVu2yW+thx4efWpwkysasXWU11Bw3M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732485AbfHZOb0 (ORCPT ); Mon, 26 Aug 2019 10:31:26 -0400 Received: from mail.kernel.org ([198.145.29.99]:41344 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726484AbfHZOb0 (ORCPT ); Mon, 26 Aug 2019 10:31:26 -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 8F8E02173E; Mon, 26 Aug 2019 14:31:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566829885; bh=S0V5XzeUw6fLtK+Xw7uttsjbYD3Xydm6LhgGRawrGX0=; h=From:To:Cc:Subject:Date:From; b=HdM+S1qfzWCubuHSz6qprslKCDToWduEWGAZnKuGrZAg3ma0tx7ElLj13ud7eZ+in btG6ByNvg67bwAvN/iGinplkOY5WKXOuTXcBA/5EJJ00R7BYBmLOsiaR/m8BlF8ZKb /b6XNqIcvqne7TeArj/U9ZqIUZx5dITtt0zKn9jQ= From: Sasha Levin To: peterz@infradead.org, will@kernel.org, jstancek@redhat.com, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, Waiman Long , dbueso@suse.de, Ingo Molnar , Sasha Levin Subject: [PATCH v5.2 1/2] locking/rwsem: Add missing ACQUIRE to read_slowpath exit when queue is empty Date: Mon, 26 Aug 2019 10:31:13 -0400 Message-Id: <20190826143114.23471-1-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jan Stancek [ Upstream commit e1b98fa316648420d0434d9ff5b92ad6609ba6c3 ] 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 Signed-off-by: Sasha Levin --- This is a backport for the v5.2 stable tree. There were multiple reports of this issue being hit. Given that there were a few changes to the code around this, I'd appreciate an ack before pulling it in. kernel/locking/rwsem-xadd.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 0b1f779572402..397dedc58432d 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -454,6 +454,8 @@ __rwsem_down_read_failed_common(struct rw_semaphore *sem, int state) * been set in the count. */ if (atomic_long_read(&sem->count) >= 0) { + /* 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); -- 2.20.1