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Date: Wed, 9 Jun 2010 17:08:52 -0700 From: Salman Qazi <sqazi@...gle.com> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: 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 3:27 PM, Linus Torvalds <torvalds@...ux-foundation.org> 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@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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