From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752491AbZHHPb0 (ORCPT ); Sat, 8 Aug 2009 11:31:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752303AbZHHPbZ (ORCPT ); Sat, 8 Aug 2009 11:31:25 -0400 Received: from hera.kernel.org ([140.211.167.34]:40021 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751235AbZHHPbY (ORCPT ); Sat, 8 Aug 2009 11:31:24 -0400 Date: Sat, 8 Aug 2009 15:27:49 GMT From: tip-bot for Darren Hart To: linux-tip-commits@vger.kernel.org Cc: linux-kernel@vger.kernel.org, dvhltc@us.ibm.com, hpa@zytor.com, mingo@redhat.com, jkacur@redhat.com, johnstul@us.ibm.com, peterz@infradead.org, dino@in.ibm.com, rostedt@goodmis.org, stable@kernel.org, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, dvhltc@us.ibm.com, linux-kernel@vger.kernel.org, jkacur@redhat.com, johnstul@us.ibm.com, peterz@infradead.org, dino@in.ibm.com, rostedt@goodmis.org, stable@kernel.org, tglx@linutronix.de, mingo@elte.hu In-Reply-To: <4A7A016C.1090002@us.ibm.com> References: <4A7A016C.1090002@us.ibm.com> Subject: [tip:core/urgent] futex: Update woken requeued futex_q lock_ptr Message-ID: Git-Commit-ID: 00235fe25eba6d3a13f3349b2e3a2d94b699a414 X-Mailer: tip-git-log-daemon MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.0 (hera.kernel.org [127.0.0.1]); Sat, 08 Aug 2009 15:27:51 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 00235fe25eba6d3a13f3349b2e3a2d94b699a414 Gitweb: http://git.kernel.org/tip/00235fe25eba6d3a13f3349b2e3a2d94b699a414 Author: Darren Hart AuthorDate: Wed, 5 Aug 2009 15:02:20 -0700 Committer: Ingo Molnar CommitDate: Sat, 8 Aug 2009 17:21:49 +0200 futex: Update woken requeued futex_q lock_ptr futex_requeue() can acquire the lock on behalf of a waiter during the requeue loop in the event of a lock steal or owner died. futex_wait_requeue_pi() cleans up the pi_state owner, using the lock_ptr to protect against concurrent access to the pi_state. The pi_state is found on the requeue target futex hash bucket so the lock_ptr needs to be updated accordingly. The problem manifested by triggering the WARN_ON in lookup_pi_state() about the pid != pi_state->owner pid. The astute reviewer will note that still exists a race between the time futex_requeue() releases hb2->lock() and the time when futex_wait_requeue_pi() acquires it. During this time the pi_state and the futex uaddr are not in sync with the rt_mutex ownership. This patch closes the window to the point where my tests now pass, but we still need to address it. Signed-off-by: Darren Hart Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Dinakar Guniguntala Cc: John Stultz Cc: John Kacur Cc: LKML-Reference: <4A7A016C.1090002@us.ibm.com> Signed-off-by: Ingo Molnar --- kernel/futex.c | 13 +++++++++---- 1 files changed, 9 insertions(+), 4 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 0672ff8..57f5a80 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1010,19 +1010,24 @@ void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1, * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue * q: the futex_q * key: the key of the requeue target futex + * hb: the hash_bucket of the requeue target futex * * During futex_requeue, with requeue_pi=1, it is possible to acquire the * target futex if it is uncontended or via a lock steal. Set the futex_q key * to the requeue target futex so the waiter can detect the wakeup on the right * futex, but remove it from the hb and NULL the rt_waiter so it can detect - * atomic lock acquisition. Must be called with the q->lock_ptr held. + * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock + * to protect access to the pi_state to fixup the owner later. Must be called + * with the q->lock_ptr held. */ static inline -void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key) +void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, + struct futex_hash_bucket *hb) { drop_futex_key_refs(&q->key); get_futex_key_refs(key); q->key = *key; + q->lock_ptr = &hb->lock; WARN_ON(plist_node_empty(&q->list)); plist_del(&q->list, &q->list.plist); @@ -1088,7 +1093,7 @@ static int futex_proxy_trylock_atomic(u32 __user *pifutex, ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, set_waiters); if (ret == 1) - requeue_pi_wake_futex(top_waiter, key2); + requeue_pi_wake_futex(top_waiter, key2, hb2); return ret; } @@ -1273,7 +1278,7 @@ retry_private: this->task, 1); if (ret == 1) { /* We got the lock. */ - requeue_pi_wake_futex(this, &key2); + requeue_pi_wake_futex(this, &key2, hb2); continue; } else if (ret) { /* -EDEADLK */