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From: Peter Zijlstra <peterz@infradead.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Waiman Long <waiman.long@hp.com>,
	tglx@linutronix.de, mingo@kernel.org, linux-arch@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	xen-devel@lists.xenproject.org, kvm@vger.kernel.org,
	paolo.bonzini@gmail.com, konrad.wilk@oracle.com,
	boris.ostrovsky@oracle.com, paulmck@linux.vnet.ibm.com,
	riel@redhat.com, torvalds@linux-foundation.org,
	raghavendra.kt@linux.vnet.ibm.com, david.vrabel@citrix.com,
	oleg@redhat.com, gleb@redhat.com, scott.norton@hp.com,
	chegu_vinod@hp.com
Subject: Re: [PATCH 10/11] qspinlock: Paravirt support
Date: Mon, 7 Jul 2014 17:20:58 +0200	[thread overview]
Message-ID: <20140707152058.GV6758@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <53A18000.8080909@redhat.com>

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On Wed, Jun 18, 2014 at 02:03:12PM +0200, Paolo Bonzini wrote:
> Il 17/06/2014 00:08, Waiman Long ha scritto:
> >>+void __pv_queue_unlock(struct qspinlock *lock)
> >>+{
> >>+	int val = atomic_read(&lock->val);
> >>+
> >>+	native_queue_unlock(lock);
> >>+
> >>+	if (val & _Q_LOCKED_SLOW)
> >>+		___pv_kick_head(lock);
> >>+}
> >>+
> >
> >Again a race can happen here between the reading and writing of the lock
> >value. I can't think of a good way to do that without using cmpxchg.
> 
> Could you just use xchg on the locked byte?

I'll have to, indeed. This is racy.

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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Waiman Long <waiman.long@hp.com>,
	linux-arch@vger.kernel.org, riel@redhat.com, gleb@redhat.com,
	kvm@vger.kernel.org, konrad.wilk@oracle.com,
	boris.ostrovsky@oracle.com, scott.norton@hp.com,
	raghavendra.kt@linux.vnet.ibm.com, paolo.bonzini@gmail.com,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org, chegu_vinod@hp.com,
	david.vrabel@citrix.com, oleg@redhat.com,
	xen-devel@lists.xenproject.org, tglx@linutronix.de,
	paulmck@linux.vnet.ibm.com, torvalds@linux-foundation.org,
	mingo@kernel.org
Subject: Re: [PATCH 10/11] qspinlock: Paravirt support
Date: Mon, 7 Jul 2014 17:20:58 +0200	[thread overview]
Message-ID: <20140707152058.GV6758@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <53A18000.8080909@redhat.com>


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On Wed, Jun 18, 2014 at 02:03:12PM +0200, Paolo Bonzini wrote:
> Il 17/06/2014 00:08, Waiman Long ha scritto:
> >>+void __pv_queue_unlock(struct qspinlock *lock)
> >>+{
> >>+	int val = atomic_read(&lock->val);
> >>+
> >>+	native_queue_unlock(lock);
> >>+
> >>+	if (val & _Q_LOCKED_SLOW)
> >>+		___pv_kick_head(lock);
> >>+}
> >>+
> >
> >Again a race can happen here between the reading and writing of the lock
> >value. I can't think of a good way to do that without using cmpxchg.
> 
> Could you just use xchg on the locked byte?

I'll have to, indeed. This is racy.

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  parent reply	other threads:[~2014-07-07 15:21 UTC|newest]

Thread overview: 191+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-06-15 12:46 [PATCH 00/11] qspinlock with paravirt support Peter Zijlstra
2014-06-15 12:46 ` Peter Zijlstra
2014-06-15 12:46 ` [PATCH 01/11] qspinlock: A simple generic 4-byte queue spinlock Peter Zijlstra
2014-06-15 12:46 ` Peter Zijlstra
2014-06-15 12:46   ` Peter Zijlstra
2014-06-16 20:49   ` Konrad Rzeszutek Wilk
2014-06-16 20:49   ` Konrad Rzeszutek Wilk
2014-06-16 20:49     ` Konrad Rzeszutek Wilk
2014-06-17 20:03     ` Konrad Rzeszutek Wilk
2014-06-17 20:03       ` Konrad Rzeszutek Wilk
2014-06-17 20:03       ` Konrad Rzeszutek Wilk
2014-06-17 20:03       ` Konrad Rzeszutek Wilk
2014-06-23 16:12       ` Peter Zijlstra
2014-06-23 16:12       ` Peter Zijlstra
2014-06-23 16:12         ` Peter Zijlstra
2014-06-23 16:20         ` Konrad Rzeszutek Wilk
2014-06-23 16:20         ` Konrad Rzeszutek Wilk
2014-06-23 16:20           ` Konrad Rzeszutek Wilk
2014-06-17 20:03     ` Konrad Rzeszutek Wilk
2014-06-23 15:56     ` Peter Zijlstra
2014-06-23 15:56     ` Peter Zijlstra
2014-06-23 15:56     ` Peter Zijlstra
2014-06-23 16:16       ` Konrad Rzeszutek Wilk
2014-06-23 16:16         ` Konrad Rzeszutek Wilk
2014-06-23 16:16       ` Konrad Rzeszutek Wilk
2014-06-17 20:05   ` Konrad Rzeszutek Wilk
2014-06-17 20:05     ` Konrad Rzeszutek Wilk
2014-06-17 20:05     ` Konrad Rzeszutek Wilk
2014-06-17 20:05     ` Konrad Rzeszutek Wilk
2014-06-23 16:26     ` Peter Zijlstra
2014-06-23 16:26       ` Peter Zijlstra
2014-06-23 16:45       ` Konrad Rzeszutek Wilk
2014-06-23 16:45         ` Konrad Rzeszutek Wilk
2014-06-23 16:45       ` Konrad Rzeszutek Wilk
2014-06-23 16:26     ` Peter Zijlstra
2014-06-17 20:05   ` Konrad Rzeszutek Wilk
2014-06-15 12:46 ` [PATCH 02/11] qspinlock, x86: Enable x86-64 to use " Peter Zijlstra
2014-06-15 12:46 ` Peter Zijlstra
2014-06-15 12:46 ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 03/11] qspinlock: Add pending bit Peter Zijlstra
2014-06-15 12:47 ` Peter Zijlstra
2014-06-15 12:47   ` Peter Zijlstra
2014-06-17 20:36   ` Konrad Rzeszutek Wilk
2014-06-17 20:36   ` Konrad Rzeszutek Wilk
2014-06-17 20:36     ` Konrad Rzeszutek Wilk
2014-06-17 20:51     ` Waiman Long
2014-06-17 20:51     ` Waiman Long
2014-06-17 20:51       ` Waiman Long
2014-06-17 21:07       ` Konrad Rzeszutek Wilk
2014-06-17 21:07       ` Konrad Rzeszutek Wilk
2014-06-17 21:07         ` Konrad Rzeszutek Wilk
2014-06-17 21:10         ` Konrad Rzeszutek Wilk
2014-06-17 21:10           ` Konrad Rzeszutek Wilk
2014-06-17 22:25           ` Waiman Long
2014-06-17 22:25             ` Waiman Long
2014-06-17 22:25           ` Waiman Long
2014-06-17 21:10         ` Konrad Rzeszutek Wilk
2014-06-24  8:24         ` Peter Zijlstra
2014-06-24  8:24           ` Peter Zijlstra
2014-06-24  8:24         ` Peter Zijlstra
2014-06-18 11:29     ` Paolo Bonzini
2014-06-18 11:29     ` Paolo Bonzini
2014-06-18 11:29       ` Paolo Bonzini
2014-06-18 13:36       ` Konrad Rzeszutek Wilk
2014-06-18 13:36       ` Konrad Rzeszutek Wilk
2014-06-18 13:36         ` Konrad Rzeszutek Wilk
2014-06-23 16:35     ` Peter Zijlstra
2014-06-23 16:35     ` Peter Zijlstra
2014-06-23 16:35       ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 04/11] qspinlock: Extract out the exchange of tail code word Peter Zijlstra
2014-06-15 12:47 ` Peter Zijlstra
2014-06-17 20:55   ` Konrad Rzeszutek Wilk
2014-06-17 20:55     ` Konrad Rzeszutek Wilk
2014-06-18 11:37     ` Paolo Bonzini
2014-06-18 11:37     ` Paolo Bonzini
2014-06-18 11:37       ` Paolo Bonzini
2014-06-18 13:50       ` Konrad Rzeszutek Wilk
2014-06-18 13:50       ` Konrad Rzeszutek Wilk
2014-06-18 13:50         ` Konrad Rzeszutek Wilk
2014-06-18 15:46         ` Waiman Long
2014-06-18 15:46           ` Waiman Long
2014-06-18 15:49           ` Paolo Bonzini
2014-06-18 15:49             ` Paolo Bonzini
2014-06-18 15:49           ` Paolo Bonzini
2014-06-18 16:02           ` Konrad Rzeszutek Wilk
2014-06-18 16:02           ` Konrad Rzeszutek Wilk
2014-06-18 16:02             ` Konrad Rzeszutek Wilk
2014-06-18 15:46         ` Waiman Long
2014-06-24 10:47       ` Peter Zijlstra
2014-06-24 10:47         ` Peter Zijlstra
2014-06-24 10:47       ` Peter Zijlstra
2014-06-17 20:55   ` Konrad Rzeszutek Wilk
2014-06-15 12:47 ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 05/11] qspinlock: Optimize for smaller NR_CPUS Peter Zijlstra
2014-06-15 12:47 ` Peter Zijlstra
2014-06-15 12:47   ` Peter Zijlstra
2014-06-18 11:39   ` Paolo Bonzini
2014-06-18 11:39   ` Paolo Bonzini
2014-06-18 11:39     ` Paolo Bonzini
2014-07-07 14:35     ` Peter Zijlstra
2014-07-07 14:35     ` Peter Zijlstra
2014-07-07 14:35       ` Peter Zijlstra
2014-07-07 15:08       ` Paolo Bonzini
2014-07-07 15:08       ` Paolo Bonzini
2014-07-07 15:08       ` Paolo Bonzini
2014-07-07 15:35         ` Peter Zijlstra
2014-07-07 15:35           ` Peter Zijlstra
2014-07-07 16:10           ` Paolo Bonzini
2014-07-07 16:10             ` Paolo Bonzini
2014-07-07 16:10           ` Paolo Bonzini
2014-07-07 15:35         ` Peter Zijlstra
2014-06-18 15:57   ` Konrad Rzeszutek Wilk
2014-06-18 15:57     ` Konrad Rzeszutek Wilk
2014-07-07 14:33     ` Peter Zijlstra
2014-07-07 14:33     ` Peter Zijlstra
2014-07-07 14:33       ` Peter Zijlstra
2014-06-18 15:57   ` Konrad Rzeszutek Wilk
2014-06-15 12:47 ` [PATCH 06/11] qspinlock: Optimize pending bit Peter Zijlstra
2014-06-15 12:47 ` Peter Zijlstra
2014-06-15 12:47 ` Peter Zijlstra
2014-06-18 11:42   ` Paolo Bonzini
2014-06-18 11:42   ` Paolo Bonzini
2014-06-18 11:42     ` Paolo Bonzini
2014-06-15 12:47 ` [PATCH 07/11] qspinlock: Use a simple write to grab the lock, if applicable Peter Zijlstra
2014-06-15 12:47   ` Peter Zijlstra
2014-06-18 16:36   ` Konrad Rzeszutek Wilk
2014-06-18 16:36   ` Konrad Rzeszutek Wilk
2014-06-18 16:36     ` Konrad Rzeszutek Wilk
2014-07-07 14:51     ` Peter Zijlstra
2014-07-07 14:51     ` Peter Zijlstra
2014-07-07 14:51       ` Peter Zijlstra
2014-06-15 12:47 ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 08/11] qspinlock: Revert to test-and-set on hypervisors Peter Zijlstra
2014-06-15 12:47 ` Peter Zijlstra
2014-06-15 12:47   ` Peter Zijlstra
2014-06-16 21:57   ` Waiman Long
2014-06-16 21:57   ` Waiman Long
2014-06-16 21:57   ` Waiman Long
2014-06-18 16:40   ` Konrad Rzeszutek Wilk
2014-06-18 16:40   ` Konrad Rzeszutek Wilk
2014-06-18 16:40     ` Konrad Rzeszutek Wilk
2014-06-15 12:47 ` [PATCH 09/11] pvqspinlock, x86: Rename paravirt_ticketlocks_enabled Peter Zijlstra
2014-06-18 16:43   ` Konrad Rzeszutek Wilk
2014-06-18 16:43   ` Konrad Rzeszutek Wilk
2014-06-18 16:43     ` Konrad Rzeszutek Wilk
2014-06-15 12:47 ` Peter Zijlstra
2014-06-15 12:47 ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 10/11] qspinlock: Paravirt support Peter Zijlstra
2014-06-15 12:47 ` Peter Zijlstra
2014-06-15 12:47   ` Peter Zijlstra
2014-06-16 22:08   ` Waiman Long
2014-06-18 12:03     ` Paolo Bonzini
2014-06-18 12:03       ` Paolo Bonzini
2014-06-18 15:26       ` Waiman Long
2014-06-18 15:26       ` Waiman Long
2014-06-18 15:26         ` Waiman Long
2014-07-07 15:20       ` Peter Zijlstra
2014-07-07 15:20       ` Peter Zijlstra [this message]
2014-07-07 15:20         ` Peter Zijlstra
2014-06-18 12:03     ` Paolo Bonzini
2014-07-07 15:20     ` Peter Zijlstra
2014-07-07 15:20     ` Peter Zijlstra
2014-07-07 15:20       ` Peter Zijlstra
2014-06-16 22:08   ` Waiman Long
2014-06-17  0:53   ` Waiman Long
2014-06-17  0:53     ` Waiman Long
2014-06-17  0:53   ` Waiman Long
2014-06-18 12:04   ` Paolo Bonzini
2014-06-18 12:04   ` Paolo Bonzini
2014-06-18 12:04     ` Paolo Bonzini
2014-06-20 13:46   ` Konrad Rzeszutek Wilk
2014-06-20 13:46   ` Konrad Rzeszutek Wilk
2014-06-20 13:46     ` Konrad Rzeszutek Wilk
2014-07-07 15:27     ` Peter Zijlstra
2014-07-15 14:23       ` Konrad Rzeszutek Wilk
2014-07-15 14:23       ` Konrad Rzeszutek Wilk
2014-07-15 14:23         ` Konrad Rzeszutek Wilk
2014-07-07 15:27     ` Peter Zijlstra
2014-07-07 15:27     ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 11/11] qspinlock, kvm: Add paravirt support Peter Zijlstra
2014-06-22 16:36   ` Raghavendra K T
2014-06-22 16:36     ` Raghavendra K T
2014-07-07 15:23     ` Peter Zijlstra
2014-07-07 15:23       ` Peter Zijlstra
2014-07-07 15:23     ` Peter Zijlstra
2014-06-22 16:36   ` Raghavendra K T
2014-06-15 12:47 ` Peter Zijlstra
2014-06-15 12:47 ` Peter Zijlstra
2014-06-16 20:52 ` [PATCH 00/11] qspinlock with " Konrad Rzeszutek Wilk
2014-06-16 20:52   ` Konrad Rzeszutek Wilk
2014-06-16 20:52 ` Konrad Rzeszutek Wilk

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