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

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Message-ID: <20100615032608.GB30479@drongo>
Date:	Tue, 15 Jun 2010 13:26:08 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	tytso@....edu, Salman <sqazi@...gle.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	tytso@...gle.com, torvalds@...ux-foundation.org, walken@...gle.com,
	Chen Liqin <liqin.chen@...plusct.com>,
	Lennox Wu <lennox.wu@...il.com>
Subject: Re: [PATCH] Fix a race in pid generation that causes pids to be
 reused immediately.

On Mon, Jun 14, 2010 at 06:55:56PM -0700, Andrew Morton wrote:

> > kernel/sched_clock.c:   if (cmpxchg64(&scd->clock, old_clock, clock) != old_cloc
> 
> I guess that'll flush out any stragglers.

And break most non-x86 32-bit architectures, including 32-bit powerpc.
Fortunately that code is only used if CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
is set, and it looks like only x86 and ia64 set it.

Paul.
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