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From: Tejun Heo <tj@kernel.org>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Amit Shah <amit.shah@redhat.com>,
	netdev@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org,
	"Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH RFC] virtio_net: fix refill related races
Date: Wed, 14 Dec 2011 15:54:12 -0800	[thread overview]
Message-ID: <20111214235412.GA29835@google.com> (raw)
In-Reply-To: <87iplltd0g.fsf@rustcorp.com.au>

Hello, Rusty.

On Tue, Dec 13, 2011 at 01:05:11PM +1030, Rusty Russell wrote:
> Both places where we call:
> 
> 	cancel_delayed_work_sync(&vi->refill);
> 
> Do not actually guarantee that vi->refill isn't running, because it
> can requeue itself.  A 'bool no_more_refill' field seems like the
> simplest fix for this, but I don't think it's sufficient.
> 
> Tejun, is this correct?  What's the correct way to synchronously stop a
> delayed_work which can "schedule_delayed_work(&vi->refill, HZ/2);" on
> itself?

cancel_delayed_work_sync() itself should be good enough.  It first
steals the pending state and then waits for it to finish if in-flight.
Queueing itself afterwards becomes noop.

Thanks.

-- 
tejun

WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj@kernel.org>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	Amit Shah <amit.shah@redhat.com>,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC] virtio_net: fix refill related races
Date: Wed, 14 Dec 2011 15:54:12 -0800	[thread overview]
Message-ID: <20111214235412.GA29835@google.com> (raw)
In-Reply-To: <87iplltd0g.fsf@rustcorp.com.au>

Hello, Rusty.

On Tue, Dec 13, 2011 at 01:05:11PM +1030, Rusty Russell wrote:
> Both places where we call:
> 
> 	cancel_delayed_work_sync(&vi->refill);
> 
> Do not actually guarantee that vi->refill isn't running, because it
> can requeue itself.  A 'bool no_more_refill' field seems like the
> simplest fix for this, but I don't think it's sufficient.
> 
> Tejun, is this correct?  What's the correct way to synchronously stop a
> delayed_work which can "schedule_delayed_work(&vi->refill, HZ/2);" on
> itself?

cancel_delayed_work_sync() itself should be good enough.  It first
steals the pending state and then waits for it to finish if in-flight.
Queueing itself afterwards becomes noop.

Thanks.

-- 
tejun

  reply	other threads:[~2011-12-14 23:54 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-12-07 15:21 [PATCH RFC] virtio_net: fix refill related races Michael S. Tsirkin
2011-12-07 15:21 ` Michael S. Tsirkin
2011-12-08  4:37 ` Rusty Russell
2011-12-08  4:37   ` Rusty Russell
2011-12-08  4:37   ` Rusty Russell
2011-12-11 14:44   ` Michael S. Tsirkin
2011-12-11 14:44     ` Michael S. Tsirkin
2011-12-11 22:55     ` Rusty Russell
2011-12-11 22:55       ` Rusty Russell
2011-12-12 11:54       ` Michael S. Tsirkin
2011-12-12 11:54         ` Michael S. Tsirkin
2011-12-13  2:35         ` Rusty Russell
2011-12-13  2:35           ` Rusty Russell
2011-12-14 23:54           ` Tejun Heo [this message]
2011-12-14 23:54             ` Tejun Heo
2011-12-20 19:09           ` Michael S. Tsirkin
2011-12-20 19:09             ` Michael S. Tsirkin
2011-12-20 19:09             ` Tejun Heo
2011-12-20 19:09               ` Tejun Heo
2011-12-20 19:30               ` Michael S. Tsirkin
2011-12-20 19:30                 ` Michael S. Tsirkin
2011-12-20 19:31                 ` Tejun Heo
2011-12-20 19:31                   ` Tejun Heo
2011-12-20 19:45                   ` Michael S. Tsirkin
2011-12-20 19:45                     ` Michael S. Tsirkin
2011-12-20 23:43                     ` Rusty Russell
2011-12-20 23:43                       ` Rusty Russell
2011-12-21  9:06                       ` Michael S. Tsirkin
2011-12-21  9:06                         ` Michael S. Tsirkin
2011-12-22  3:53                         ` Rusty Russell
2011-12-22  3:53                           ` Rusty Russell

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