Re: [PATCH] Fix a race in pid generation that causes pids to be reused immediately.

[Salman Qazi]

On Wed, Jun 9, 2010 at 3:27 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
>
> On Wed, 9 Jun 2010, Linus Torvalds wrote:
>>
>> Quite possibly. I'd worry about the overflow case a bit, but it's
>> certainly going to get the right value when base << MAX_INT.
>
> Having given it a couple of seconds more thought, I don't think there is
> an overflow case either. All of a/b/base are guaranteed to be non-negative
> (or our pid code is in worse trouble anyway), so there is no overflow
> possible. So yes. Just comparing a-base < b-base should always be safe

I don't think this gives the right answer in the a < base < b  case.
Here a - base < 0 and
b - base > 0.  But we really want b to be before a, since a has rolled
over further than b.  I think
the right solution is comparing (a - base + max_pid) % max_pid with (b
- base + max_pid) % max_pid.  Am I correct or deluded?
.
>
>                        Linus
>
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/