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

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Message-ID: <AANLkTikZx3sCFvCUWUwtMfRzMsnQ9E2UWs4XbfCw5XID@mail.gmail.com>
Date:	Thu, 10 Jun 2010 09:39:02 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Salman Qazi <sqazi@...gle.com>
Cc:	Michel Lespinasse <walken@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	akpm@...ux-foundation.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org, tytso@...gle.com
Subject: Re: [PATCH] Fix a race in pid generation that causes pids to be 
	reused immediately.

On Wed, Jun 9, 2010 at 10:55 PM, Salman Qazi <sqazi@...gle.com> wrote:
> On Wed, Jun 9, 2010 at 10:17 PM, Michel Lespinasse <walken@...gle.com> wrote:
>>
>> As shown by the three compares version, the question here does not depend on
>> the max_pid value. So, we can replace max_pid with any integer >= max_pid
>> without changing the result.

I like the logical argument, and cannot fault it.

>> This is nice because, replacing max_pid with
>> 2^32, the expression simplifies to:
>>
>> (unsigned)(a - base) < (unsigned)(b - base)
>>
>> I think I like this form after all :)

Sounds right to me.

> I don't mind doing this, if nobody disagrees.  Should be fine with a
> comment on top explaining the intention?

Yes. And lots of testing (including, very much, the whole max_pid
roll-over, of course). The logic of it all seems impeccable, but
nothing beats testing.

Thanks,
             Linus
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