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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 6CD5FC47404 for ; Mon, 7 Oct 2019 14:16:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 43BC0206BB for ; Mon, 7 Oct 2019 14:16:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728132AbfJGOQw (ORCPT ); Mon, 7 Oct 2019 10:16:52 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:44030 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726334AbfJGOQv (ORCPT ); Mon, 7 Oct 2019 10:16:51 -0400 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1iHTod-0005Li-06; Mon, 07 Oct 2019 16:16:47 +0200 Date: Mon, 7 Oct 2019 16:16:46 +0200 From: Sebastian Andrzej Siewior To: LKML Cc: linux-rt-users , Steven Rostedt , Thomas Gleixner , Peter Zijlstra Subject: [PATCH RT] locking/rtmutex: Clean ->pi_blocked_on in the error case Message-ID: <20191007141646.2qjo3d6pnzdrlr5l@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra The function rt_mutex_wait_proxy_lock() cleans ->pi_blocked_on in case of failure (timeout, signal). The same cleanup is required in __rt_mutex_start_proxy_lock(). In both the cases the tasks was interrupted by a signal or timeout while acquiring the lock and after the interruption it longer blocks on the lock. Fixes: 1a1fb985f2e2b ("futex: Handle early deadlock return correctly") Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Sebastian Andrzej Siewior --- This means I'm going to revert the raw_spinlock_t changes to futex_hash_bucket, add back all futex fixes we had and put this one on top. kernel/locking/rtmutex.c | 43 +++++++++++++++++++++++----------------- 1 file changed, 25 insertions(+), 18 deletions(-) diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 0649a33fb7e6c..bb5c09c49c504 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -2321,6 +2321,26 @@ void rt_mutex_proxy_unlock(struct rt_mutex *lock, rt_mutex_set_owner(lock, NULL); } +static void fixup_rt_mutex_blocked(struct rt_mutex *lock) +{ + struct task_struct *tsk = current; + /* + * RT has a problem here when the wait got interrupted by a timeout + * or a signal. task->pi_blocked_on is still set. The task must + * acquire the hash bucket lock when returning from this function. + * + * If the hash bucket lock is contended then the + * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in + * task_blocks_on_rt_mutex() will trigger. This can be avoided by + * clearing task->pi_blocked_on which removes the task from the + * boosting chain of the rtmutex. That's correct because the task + * is not longer blocked on it. + */ + raw_spin_lock(&tsk->pi_lock); + tsk->pi_blocked_on = NULL; + raw_spin_unlock(&tsk->pi_lock); +} + /** * __rt_mutex_start_proxy_lock() - Start lock acquisition for another task * @lock: the rt_mutex to take @@ -2393,6 +2413,9 @@ int __rt_mutex_start_proxy_lock(struct rt_mutex *lock, ret = 0; } + if (ret) + fixup_rt_mutex_blocked(lock); + debug_rt_mutex_print_deadlock(waiter); return ret; @@ -2473,7 +2496,6 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock, struct hrtimer_sleeper *to, struct rt_mutex_waiter *waiter) { - struct task_struct *tsk = current; int ret; raw_spin_lock_irq(&lock->wait_lock); @@ -2485,23 +2507,8 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock, * have to fix that up. */ fixup_rt_mutex_waiters(lock); - /* - * RT has a problem here when the wait got interrupted by a timeout - * or a signal. task->pi_blocked_on is still set. The task must - * acquire the hash bucket lock when returning from this function. - * - * If the hash bucket lock is contended then the - * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in - * task_blocks_on_rt_mutex() will trigger. This can be avoided by - * clearing task->pi_blocked_on which removes the task from the - * boosting chain of the rtmutex. That's correct because the task - * is not longer blocked on it. - */ - if (ret) { - raw_spin_lock(&tsk->pi_lock); - tsk->pi_blocked_on = NULL; - raw_spin_unlock(&tsk->pi_lock); - } + if (ret) + fixup_rt_mutex_blocked(lock); raw_spin_unlock_irq(&lock->wait_lock); -- 2.23.0