From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755559AbZHDORG (ORCPT ); Tue, 4 Aug 2009 10:17:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755527AbZHDORF (ORCPT ); Tue, 4 Aug 2009 10:17:05 -0400 Received: from hera.kernel.org ([140.211.167.34]:55142 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755373AbZHDORC (ORCPT ); Tue, 4 Aug 2009 10:17:02 -0400 Date: Tue, 4 Aug 2009 14:15:51 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, rostedt@goodmis.org, peterz@infradead.org, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, dvhltc@us.ibm.com, linux-kernel@vger.kernel.org, rostedt@goodmis.org, peterz@infradead.org, tglx@linutronix.de, mingo@elte.hu In-Reply-To: <4A737C2A.9090001@us.ibm.com> References: <4A737C2A.9090001@us.ibm.com> Subject: [tip:core/futexes] futex: Correct futex_wait_requeue_pi() commentary Message-ID: Git-Commit-ID: cc6db4e60116c1f76577b6850a35ae7de69a95b6 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]); Tue, 04 Aug 2009 14:15:51 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: cc6db4e60116c1f76577b6850a35ae7de69a95b6 Gitweb: http://git.kernel.org/tip/cc6db4e60116c1f76577b6850a35ae7de69a95b6 Author: Darren Hart AuthorDate: Fri, 31 Jul 2009 16:20:10 -0700 Committer: Ingo Molnar CommitDate: Tue, 4 Aug 2009 15:59:14 +0200 futex: Correct futex_wait_requeue_pi() commentary The state machine described in the comments wasn't updated with a follow-on fix. Address that and cleanup the corresponding commentary in the function. Signed-off-by: Darren Hart Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner LKML-Reference: <4A737C2A.9090001@us.ibm.com> Signed-off-by: Ingo Molnar --- kernel/futex.c | 23 ++++++++++------------- 1 files changed, 10 insertions(+), 13 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 0672ff8..d077201 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -2102,11 +2102,11 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, * We call schedule in futex_wait_queue_me() when we enqueue and return there * via the following: * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() - * 2) wakeup on uaddr2 after a requeue and subsequent unlock - * 3) signal (before or after requeue) - * 4) timeout (before or after requeue) + * 2) wakeup on uaddr2 after a requeue + * 3) signal + * 4) timeout * - * If 3, we setup a restart_block with futex_wait_requeue_pi() as the function. + * If 3, cleanup and return -ERESTARTNOINTR. * * If 2, we may then block on trying to take the rt_mutex and return via: * 5) successful lock @@ -2114,7 +2114,7 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, * 7) timeout * 8) other lock acquisition failure * - * If 6, we setup a restart_block with futex_lock_pi() as the function. + * If 6, return -EWOULDBLOCK (restarting the syscall would do the same). * * If 4 or 7, we cleanup and return with -ETIMEDOUT. * @@ -2232,14 +2232,11 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared, rt_mutex_unlock(pi_mutex); } else if (ret == -EINTR) { /* - * We've already been requeued, but we have no way to - * restart by calling futex_lock_pi() directly. We - * could restart the syscall, but that will look at - * the user space value and return right away. So we - * drop back with EWOULDBLOCK to tell user space that - * "val" has been changed. That's the same what the - * restart of the syscall would do in - * futex_wait_setup(). + * We've already been requeued, but cannot restart by calling + * futex_lock_pi() directly. We could restart this syscall, but + * it would detect that the user space "val" changed and return + * -EWOULDBLOCK. Save the overhead of the restart and return + * -EWOULDBLOCK directly. */ ret = -EWOULDBLOCK; }