From: Jason Low <jason.low2@hp.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Waiman Long <Waiman.Long@hp.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Rik van Riel <riel@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Davidlohr Bueso <davidlohr@hp.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Andi Kleen <andi@firstfloor.org>,
"Chandramouleeswaran, Aswin" <aswin@hp.com>,
"Norton, Scott J" <scott.norton@hp.com>,
chegu_vinod@hp.com
Subject: Re: [RFC][PATCH v2 5/5] mutex: Give spinners a chance to spin_on_owner if need_resched() triggered while queued
Date: Sun, 02 Feb 2014 13:01:23 -0800 [thread overview]
Message-ID: <1391374883.3164.8.camel@j-VirtualBox> (raw)
In-Reply-To: <20140131200825.GS5002@laptop.programming.kicks-ass.net>
On Fri, 2014-01-31 at 21:08 +0100, Peter Zijlstra wrote:
> On Fri, Jan 31, 2014 at 12:01:37PM -0800, Jason Low wrote:
> > Currently still getting soft lockups with the updated version.
>
> Bugger.. ok clearly I need to think harder still. I'm fairly sure this
> cancelation can work though, just seems tricky to get right :-)
Ok, I believe I have found a race condition between m_spin_lock() and
m_spin_unlock().
In m_spin_unlock(), we do "next = ACCESS_ONCE(node->next)". Then, if
next is not NULL, we proceed to set next->locked to 1.
A thread in m_spin_lock() in the unqueue path could execute
"next = cmpxchg(&prev->next, node, NULL)" after the thread in
m_spin_unlock() accesses its node->next and finds that it is not NULL.
Then, the thread in m_spin_lock() could check !node->locked before
the thread in m_spin_unlock() sets next->locked to 1.
The following addition change was able to solve the initial lockups that were
occurring when running fserver on a 2 socket box.
---
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 9eb4dbe..e71a84a 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -513,8 +513,13 @@ static void m_spin_unlock(struct m_spinlock **lock)
return;
next = ACCESS_ONCE(node->next);
- if (unlikely(next))
- break;
+
+ if (unlikely(next)) {
+ next = cmpxchg(&node->next, next, NULL);
+
+ if (next)
+ break;
+ }
arch_mutex_cpu_relax();
}
next prev parent reply other threads:[~2014-02-02 21:01 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-28 19:13 [PATCH v2 0/5] mutex: Mutex scalability patches Jason Low
2014-01-28 19:13 ` [PATCH v2 1/5] mutex: In mutex_can_spin_on_owner(), return false if task need_resched() Jason Low
2014-01-28 20:20 ` Paul E. McKenney
2014-01-28 22:01 ` Jason Low
2014-01-28 21:09 ` Davidlohr Bueso
2014-03-11 12:41 ` [tip:core/locking] locking/mutexes: Return false if task need_resched() in mutex_can_spin_on_owner() tip-bot for Jason Low
2014-01-28 19:13 ` [PATCH v2 2/5] mutex: Modify the way optimistic spinners are queued Jason Low
2014-01-28 20:23 ` Paul E. McKenney
2014-01-28 20:24 ` Paul E. McKenney
2014-01-28 21:17 ` Davidlohr Bueso
2014-01-28 22:10 ` Jason Low
2014-02-02 21:58 ` Paul E. McKenney
2014-03-11 12:41 ` [tip:core/locking] locking/mutexes: " tip-bot for Jason Low
2014-03-11 15:24 ` Jason Low
2014-03-11 15:33 ` Peter Zijlstra
2014-01-28 19:13 ` [PATCH v2 3/5] mutex: Unlock the mutex without the wait_lock Jason Low
2014-03-11 12:41 ` [tip:core/locking] locking/mutexes: " tip-bot for Jason Low
2014-03-12 12:24 ` Peter Zijlstra
2014-03-12 18:44 ` Jason Low
2014-03-13 7:28 ` [tip:core/locking] locking/mutex: Fix debug checks tip-bot for Peter Zijlstra
2014-01-28 19:13 ` [RFC][PATCH v2 4/5] mutex: Disable preemtion between modifying lock->owner and locking/unlocking mutex Jason Low
2014-01-28 20:54 ` Peter Zijlstra
2014-01-28 22:17 ` Jason Low
2014-01-28 19:13 ` [RFC][PATCH v2 5/5] mutex: Give spinners a chance to spin_on_owner if need_resched() triggered while queued Jason Low
2014-01-28 21:07 ` Peter Zijlstra
2014-01-28 22:51 ` Jason Low
2014-01-29 11:51 ` Peter Zijlstra
2014-01-31 3:29 ` Jason Low
2014-01-31 14:09 ` Peter Zijlstra
2014-01-31 20:01 ` Jason Low
2014-01-31 20:08 ` Peter Zijlstra
2014-02-02 21:01 ` Jason Low [this message]
2014-02-02 21:12 ` Peter Zijlstra
2014-02-03 18:39 ` Jason Low
2014-02-03 19:25 ` Peter Zijlstra
2014-02-03 20:55 ` Jason Low
2014-02-03 21:06 ` Peter Zijlstra
2014-02-03 21:56 ` Jason Low
2014-02-04 7:13 ` Jason Low
2014-02-02 22:02 ` Paul E. McKenney
2014-02-02 20:02 ` Peter Zijlstra
2014-02-05 21:44 ` Waiman Long
2014-02-06 14:04 ` Peter Zijlstra
2014-02-06 18:45 ` Waiman Long
2014-02-06 20:10 ` Norton, Scott J
2014-02-10 17:01 ` Peter Zijlstra
2014-02-06 17:44 ` Jason Low
2014-02-06 18:37 ` Waiman Long
2014-01-28 21:08 ` [PATCH v2 0/5] mutex: Mutex scalability patches Davidlohr Bueso
2014-01-28 23:11 ` Jason Low
2014-02-06 14:52 [RFC][PATCH v2 5/5] mutex: Give spinners a chance to spin_on_owner if need_resched() triggered while queued Daniel J Blueman
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