Re: [ 67/75] ipw2200: Fix race condition in the command completion acknowledge

Ben Hutchings
2012-05-08T00:14:26Z

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On Mon, 2012-05-07 at 16:45 -0700, Stanislav Yakovlev wrote:
> On 7 May 2012 07:37, Ben Hutchings <ben@decadent.org.uk> wrote:
> > On Fri, 2012-05-04 at 13:43 -0700, Greg KH wrote:
> >> 3.3-stable review patch. If anyone has any objections, please let me know.
> >>
> >> ------------------
> >>
> >> From: Stanislav Yakovlev <stas.yakovlev@gmail.com>
> >>
> >> commit dd447319895d0c0af423e483d9b63f84f3f8869a upstream.
> >>
> >> Driver incorrectly validates command completion: instead of waiting
> >> for a command to be acknowledged it continues execution. Most of the
> >> time driver gets acknowledge of the command completion in a tasklet
> >> before it executes the next one. But sometimes it sends the next
> >> command before it gets acknowledge for the previous one. In such a
> >> case one of the following error messages appear in the log:
> > [...]
> >> + now = jiffies;
> >> + end = now + HOST_COMPLETE_TIMEOUT;
> >> +again:
> >> rc = wait_event_interruptible_timeout(priv->wait_command_queue,
> >> !(priv->
> >> status & STATUS_HCMD_ACTIVE),
> >> - HOST_COMPLETE_TIMEOUT);
> >> + end - now);
> >> + if (rc < 0) {
> >> + now = jiffies;
> >> + if (time_before(now, end))
> >> + goto again;
> >> + rc = 0;
> >> + }
> > [...]
> >
> > If you don't want the wait to be interrupted, use wait_event_timeout()
> > instead of this ridiculous loop!
>
> Usually "modprobe ipw2200" takes less than a second, and after
> switching to wait_event_timeout it will take more than 10 seconds. We
> can not decrease the waiting timeout because we want to keep it big
> enough for the worst case(when the firmware did not reply).
>
> There is a relevant discussion on lklm:
> https://lkml.org/lkml/2008/9/25/2
> https://lkml.org/lkml/2008/9/26/194

That's irrelevant: you aren't letting userland handle the signal here,
so you should use wait_event_timeout() and no loop.

Ben.

--
Ben Hutchings
Life is what happens to you while you're busy making other plans.
- John Lennon

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