Hi,
On Wed, Apr 27 2011, Andrei Warkentin wrote:
> On Wed, Apr 27, 2011 at 8:23 AM, Mark Brown
> <broo...@opensource.wolfsonmicro.com> wrote:
>> I've had this pair of patches sitting in my tree for a while now (I
>> believe they were previously posted) providing stability improvements in
>> sdhci on my systems. Having looked through the code I believe but have
>> not confirmed that the issue is that the timeout is racing with an
>> actual completion of a pending task - both paths will trigger the
>> tasklet, and if you trigger a tasklet while it is running this causes it
>> to be rescheduled. The result will be that the tasklet gets run a
>> second time with no work pending for it.
>>
>> I'm not convinced that these are the best fixes (it feels like we should
>> instead be closing the races down) but I don't really have time to come
>> up with something better myself right now so I'm pushing them out as-is
>> for comment.
>
> So the timeout interrupt occurs after even though the command
> succeeds? Am I interpreting that correctly?
No, I think Mark's saying there's a race of:
* the successful completion interrupt fires, and
* the host timer fires to signify timeout due to *lack* of an interrupt
(via sdhci_timeout_timer()). i.e., the completion interrupt fires
very close to the timeout period.
Both cases call tasklet_schedule(&host->finish_tasklet), and if you
manage to schedule a tasklet while it's already running, it runs again
after it completes -- but during the first run we set host->mrq->cmd to
NULL, so then it oopses on the second run.
We could consider taking Mark's first patch and also adding to the top:
/*
* If we get scheduled twice concurrently, this tasklet will
* be run again afterwards but without any active request.
*/
if (!host->mrq)
return;
.. and pushing to .39 with a stable@ tag.
- Chris.
--
Chris Ball <c...@laptop.org> <http://printf.net/>
One Laptop Per Child
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