Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757374Ab0FJAI7 (ORCPT ); Wed, 9 Jun 2010 20:08:59 -0400 Received: from smtp-out.google.com ([74.125.121.35]:6982 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754041Ab0FJAI5 convert rfc822-to-8bit (ORCPT ); Wed, 9 Jun 2010 20:08:57 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:date:message-id:subject:from:to: cc:content-type:content-transfer-encoding; b=v/QjJf4JH/qSZmUliDwkyacmVRQSsm8notrrY1ZlVQbRIMEwZ3Ca53coLBrDE6Ffs YsOiqskMQ3R4INmzLTDOw== MIME-Version: 1.0 In-Reply-To: References: <20100609210014.7464.92234.stgit@bumblebee1.mtv.corp.google.com> <1276119207.1745.154.camel@laptop> Date: Wed, 9 Jun 2010 17:08:52 -0700 Message-ID: Subject: Re: [PATCH] Fix a race in pid generation that causes pids to be reused immediately. From: Salman Qazi To: Linus Torvalds Cc: Peter Zijlstra , akpm@linux-foundation.org, mingo@elte.hu, linux-kernel@vger.kernel.org, tytso@google.com Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1174 Lines: 31 On Wed, Jun 9, 2010 at 3:27 PM, Linus Torvalds 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/