From: Peter Hurley <peter@hurleysoftware.com>
To: Tejun Heo <tj@kernel.org>
Cc: laijs@cn.fujitsu.com, linux-kernel@vger.kernel.org,
Stefan Richter <stefanr@s5r6.in-berlin.de>,
linux1394-devel@lists.sourceforge.net,
Chris Boot <bootc@bootc.net>,
linux-scsi@vger.kernel.org, target-devel@vger.kernel.org
Subject: Re: [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK
Date: Fri, 21 Feb 2014 00:13:16 -0500 [thread overview]
Message-ID: <5306E06C.5020805@hurleysoftware.com> (raw)
In-Reply-To: <20140221021341.GG6897@htj.dyndns.org>
On 02/20/2014 09:13 PM, Tejun Heo wrote:
> On Thu, Feb 20, 2014 at 09:07:27PM -0500, Peter Hurley wrote:
>> On 02/20/2014 08:59 PM, Tejun Heo wrote:
>>> Hello,
>>>
>>> On Thu, Feb 20, 2014 at 08:44:46PM -0500, Peter Hurley wrote:
>>>>> +static void fw_device_workfn(struct work_struct *work)
>>>>> +{
>>>>> + struct fw_device *device = container_of(to_delayed_work(work),
>>>>> + struct fw_device, work);
>>>>
>>>> I think this needs an smp_rmb() here.
>>>
>>> The patch is equivalent transformation and the whole thing is
>>> guaranteed to have gone through pool->lock. No explicit rmb
>>> necessary.
>>
>> The spin_unlock_irq(&pool->lock) only guarantees completion of
>> memory operations _before_ the unlock; memory operations which occur
>> _after_ the unlock may be speculated before the unlock.
>>
>> IOW, unlock is not a memory barrier for operations that occur after.
>
> It's not just unlock. It's lock / unlock pair on the same lock from
> both sides. Nothing can sip through that.
CPU 0 | CPU 1
|
INIT_WORK(fw_device_workfn) |
|
workfn = funcA |
queue_work_on() |
. | process_one_work()
. | ..
. | worker->current_func = work->func
. |
. | speculative load of workfn = funcA
. | .
workfn = funcB | .
queue_work_on() | .
local_irq_save() | .
test_and_set_bit() == 1 | .
| set_work_pool_and_clear_pending()
work is not queued | smp_wmb
funcB never runs | set_work_data()
| atomic_set()
| spin_unlock_irq()
|
| worker->current_func(work) @ fw_device_workfn
| workfn() @ funcA
The speculative load of workfn on CPU 1 is valid because no rmb will occur
between the load and the execution of workfn() on CPU 1.
Thus funcB will never execute because, in this circumstance, a second
worker is not queued (because PENDING had not yet been cleared).
Regards,
Peter Hurley
next prev parent reply other threads:[~2014-02-21 5:13 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-20 20:44 [PATCHSET wq/for-3.15] workqueue: remove PREPARE_[DELAYED_]WORK() Tejun Heo
2014-02-20 20:44 ` [PATCH 1/9] wireless/rt2x00: don't use PREPARE_WORK in rt2800usb.c Tejun Heo
2014-03-07 15:26 ` Tejun Heo
2014-02-20 20:44 ` [PATCH 2/9] ps3-vuart: don't use PREPARE_WORK Tejun Heo
2014-02-21 23:19 ` Geoff Levand
2014-02-20 20:44 ` [PATCH 3/9] floppy: don't use PREPARE_[DELAYED_]WORK Tejun Heo
2014-02-21 9:37 ` Jiri Kosina
2014-02-20 20:44 ` [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK Tejun Heo
2014-02-21 1:44 ` Peter Hurley
2014-02-21 1:59 ` Tejun Heo
2014-02-21 2:07 ` Peter Hurley
2014-02-21 2:13 ` Tejun Heo
2014-02-21 5:13 ` Peter Hurley [this message]
2014-02-21 10:03 ` Tejun Heo
2014-02-21 12:51 ` Peter Hurley
2014-02-21 13:06 ` Tejun Heo
2014-02-21 16:53 ` Peter Hurley
2014-02-21 16:57 ` Tejun Heo
2014-02-21 23:01 ` Peter Hurley
2014-02-21 23:18 ` Tejun Heo
2014-02-21 23:46 ` Peter Hurley
2014-02-22 14:38 ` Tejun Heo
2014-02-22 14:48 ` Peter Hurley
2014-02-22 18:43 ` James Bottomley
2014-02-22 18:48 ` Peter Hurley
2014-02-22 18:52 ` James Bottomley
2014-02-22 19:03 ` Peter Hurley
2014-02-23 1:23 ` memory-barriers.txt again (was Re: [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK) Stefan Richter
2014-02-23 16:37 ` Paul E. McKenney
2014-02-23 20:35 ` Peter Hurley
2014-02-23 23:50 ` Paul E. McKenney
2014-02-24 0:09 ` Peter Hurley
2014-02-24 16:26 ` Paul E. McKenney
2014-02-24 0:32 ` Stefan Richter
2014-02-24 16:27 ` Paul E. McKenney
2014-02-23 20:05 ` [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK James Bottomley
2014-02-23 22:32 ` Peter Hurley
2014-02-21 20:45 ` Stefan Richter
2014-03-05 21:34 ` Stefan Richter
2014-03-07 15:18 ` Tejun Heo
2014-03-07 15:26 ` [PATCH UPDATED " Tejun Heo
2014-02-20 20:44 ` [PATCH 5/9] usb: " Tejun Heo
2014-02-20 20:59 ` Greg Kroah-Hartman
2014-02-21 15:06 ` Alan Stern
2014-02-21 15:07 ` Tejun Heo
2014-02-22 14:59 ` [PATCH v2 " Tejun Heo
2014-02-22 15:14 ` Alan Stern
2014-02-22 15:20 ` Peter Hurley
2014-02-22 15:37 ` Tejun Heo
2014-02-22 23:03 ` Alan Stern
2014-02-23 4:29 ` Tejun Heo
2014-02-20 20:44 ` [PATCH 6/9] nvme: don't use PREPARE_WORK Tejun Heo
2014-03-07 15:26 ` Tejun Heo
2014-02-20 20:44 ` [PATCH 7/9] afs: " Tejun Heo
2014-02-20 22:00 ` David Howells
2014-02-20 22:46 ` Tejun Heo
2014-03-07 15:27 ` Tejun Heo
2014-02-20 20:44 ` [PATCH 8/9] staging/fwserial: " Tejun Heo
2014-02-21 15:13 ` Peter Hurley
2014-02-20 20:44 ` [PATCH 9/9] workqueue: remove PREPARE_[DELAYED_]WORK() Tejun Heo
2014-03-07 15:27 ` Tejun Heo
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