From: Paul Mackerras <paulus@samba.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: tytso@mit.edu, Salman <sqazi@google.com>,
mingo@elte.hu, linux-kernel@vger.kernel.org,
peterz@infradead.org, tytso@google.com,
torvalds@linux-foundation.org, walken@google.com,
Chen Liqin <liqin.chen@sunplusct.com>,
Lennox Wu <lennox.wu@gmail.com>
Subject: Re: [PATCH] Fix a race in pid generation that causes pids to be reused immediately.
Date: Tue, 15 Jun 2010 17:25:40 +1000 [thread overview]
Message-ID: <20100615072540.GA2530@brick.ozlabs.ibm.com> (raw)
In-Reply-To: <20100614212150.4dcb1feb.akpm@linux-foundation.org>
On Mon, Jun 14, 2010 at 09:21:50PM -0700, Andrew Morton wrote:
> If that happens then the best fix is for those architectures to get
> themselves a cmpxchg64(). Unless for some reason it's simply
> unimplementable? Worst case I guess one could use a global spinlock.
> Second-worst-case: hashed spinlocks.
Spinlocks won't help as long as you can use cmpxchg64 on any old u64
that is also accessed directly. UP can disable interrupts, of course,
but for SMP we would have to restrict cmpxchg64 to some type
(atomic64_t, maybe) for which you have to use an accessor function to
read it, so we can take the spinlock around the reads.
I suspect it isn't worth the trouble. Note that I'm talking
specifically about cmpxchg64 here, not cmpxchg.
Paul.
next prev parent reply other threads:[~2010-06-15 7:25 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-11 17:17 [PATCH] Fix a race in pid generation that causes pids to be reused immediately Salman
2010-06-11 17:44 ` Linus Torvalds
2010-06-11 22:49 ` Salman
2010-06-11 23:07 ` Linus Torvalds
2010-06-14 23:58 ` Andrew Morton
2010-06-15 0:56 ` tytso
2010-06-15 1:55 ` Andrew Morton
2010-06-15 3:26 ` Paul Mackerras
2010-06-15 4:21 ` Andrew Morton
2010-06-15 4:38 ` Eric Dumazet
2010-06-15 6:57 ` Benjamin Herrenschmidt
2010-06-15 7:25 ` Paul Mackerras [this message]
2010-06-15 12:56 ` tytso
2010-06-15 13:06 ` Kyle McMartin
2010-06-15 14:35 ` Peter Zijlstra
2010-06-15 19:37 ` Andrew Morton
2010-06-15 18:35 ` [PATCH 0/1] (Was: Fix a race in pid generation that causes pids to be reused immediately.) Oleg Nesterov
2010-06-15 18:35 ` [PATCH 1/1] pids: alloc_pidmap: remove the unnecessary boundary checks Oleg Nesterov
-- strict thread matches above, loose matches on Subject: below --
2010-06-10 21:24 [PATCH] Fix a race in pid generation that causes pids to be reused immediately Salman
2010-06-10 20:09 Salman
2010-06-10 20:38 ` tytso
2010-06-10 21:04 ` Salman Qazi
2010-06-09 21:00 Salman
2010-06-09 21:21 ` Linus Torvalds
2010-06-09 21:33 ` Peter Zijlstra
2010-06-09 22:20 ` Linus Torvalds
2010-06-09 22:27 ` Linus Torvalds
2010-06-10 0:08 ` Salman Qazi
2010-06-10 0:20 ` Linus Torvalds
[not found] ` <AANLkTilXJ0X2qxD9cNTlLayKzySEZu1HEZUWu--Go8kw@mail.gmail.com>
2010-06-10 5:55 ` Salman Qazi
2010-06-10 16:39 ` Linus Torvalds
2010-06-09 6:24 Salman
2010-06-09 6:53 ` Andi Kleen
2010-06-09 9:48 ` Ingo Molnar
2010-06-09 15:39 ` Linus Torvalds
2010-06-09 15:50 ` tytso
2010-06-09 16:06 ` Linus Torvalds
2010-06-09 17:10 ` tytso
2010-06-09 17:23 ` Linus Torvalds
2010-06-09 17:25 ` Linus Torvalds
2010-06-09 17:34 ` tytso
2010-06-09 17:43 ` Linus Torvalds
2010-06-09 17:47 ` tytso
2010-06-09 18:09 ` Salman Qazi
2010-06-09 11:49 ` Michel Lespinasse
2010-06-09 12:37 ` tytso
2010-06-09 12:17 ` tytso
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