Lucid SRU: UBUNTU: SAUCE: igb: Protect stats update

[Tim Gardner]

On 09/21/2011 08:48 AM, Stefan Bader wrote:
> On 21.09.2011 16:43, Tim Gardner wrote:
>> On 09/21/2011 08:29 AM, Stefan Bader wrote:
>>> On 21.09.2011 15:43, Tim Gardner wrote:
>>>> This patch is a partial backport of upstream
>>>> 12dcd86b75d571772512676ab301279952efc0b0. Its purpose is twofold; 1) Protect
>>>> simultaneous readers and writers, 2) refresh statistics when read from ethtool.
>>>>
>>>> rtg
>>>>
>>> Wondering whether there is any chance of a running user task holding the
>>> spinlock by that watchdog work...
>>>
>>
>> If by 'running user task' you mean the ethtool interface, then yes the lock
>> _should_ be held whilst the statistics update is in progress.
>>
> Yeah, no (if that makes any sense). I was more wondering whether the lock may be
> tried to be taken from the watchdog task (scheduled_work) while a user-space
> process does something like ethtool on the same cpu...
>

That could only happen if CONFIG_PREEMPT=y, in which case the spin lock 
logic should do the right thing.

rtg
-- 
Tim Gardner tim.gardner at canonical.com