From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linuxppc-dev@ozlabs.org, Thomas Gleixner <tglx@linutronix.de>,
akpm@linux-foundation.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] synchronize_irq needs a barrier
Date: Fri, 19 Oct 2007 14:29:03 +1000 [thread overview]
Message-ID: <1192768143.7367.98.camel@pasglop> (raw)
In-Reply-To: <20071019042025.GA9617@gondor.apana.org.au>
On Fri, 2007-10-19 at 12:20 +0800, Herbert Xu wrote:
>
> That's why I think this patch is in fact the only one that
> solves all the races in this thread. The case that it solves
> which the lock/unlock patch does not is the one where action
> flows downwards past the clearing of IRQ_INPROGRESS. I missed
> this case earlier.
>
> In fact this bug exists elsewhere too. For example, the network
> stack does this in net/sched/sch_generic.c:
>
> /* Wait for outstanding qdisc_run calls. */
> while (test_bit(__LINK_STATE_QDISC_RUNNING, &dev->state))
> yield();
>
> This has the same problem as the current synchronize_irq code.
The network stack always made be nervous with it's bitops use as locks.
Any loop of test_bit() alone as a synchronisation method, without locks
or barriers is, imho, inherently buggy.
Ben.
WARNING: multiple messages have this Message-ID (diff)
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
akpm@linux-foundation.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linuxppc-dev@ozlabs.org, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] synchronize_irq needs a barrier
Date: Fri, 19 Oct 2007 14:29:03 +1000 [thread overview]
Message-ID: <1192768143.7367.98.camel@pasglop> (raw)
In-Reply-To: <20071019042025.GA9617@gondor.apana.org.au>
On Fri, 2007-10-19 at 12:20 +0800, Herbert Xu wrote:
>
> That's why I think this patch is in fact the only one that
> solves all the races in this thread. The case that it solves
> which the lock/unlock patch does not is the one where action
> flows downwards past the clearing of IRQ_INPROGRESS. I missed
> this case earlier.
>
> In fact this bug exists elsewhere too. For example, the network
> stack does this in net/sched/sch_generic.c:
>
> /* Wait for outstanding qdisc_run calls. */
> while (test_bit(__LINK_STATE_QDISC_RUNNING, &dev->state))
> yield();
>
> This has the same problem as the current synchronize_irq code.
The network stack always made be nervous with it's bitops use as locks.
Any loop of test_bit() alone as a synchronisation method, without locks
or barriers is, imho, inherently buggy.
Ben.
next prev parent reply other threads:[~2007-10-19 4:29 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-18 1:25 [PATCH] synchronize_irq needs a barrier Benjamin Herrenschmidt
2007-10-18 1:25 ` Benjamin Herrenschmidt
2007-10-18 1:45 ` Andrew Morton
2007-10-18 1:45 ` Andrew Morton
2007-10-18 1:55 ` Benjamin Herrenschmidt
2007-10-18 1:55 ` Benjamin Herrenschmidt
2007-10-18 2:12 ` Linus Torvalds
2007-10-18 2:12 ` Linus Torvalds
2007-10-18 2:40 ` Benjamin Herrenschmidt
2007-10-18 2:40 ` Benjamin Herrenschmidt
2007-10-18 2:57 ` Benjamin Herrenschmidt
2007-10-18 2:57 ` Benjamin Herrenschmidt
2007-10-18 14:56 ` Herbert Xu
2007-10-18 14:56 ` Herbert Xu
2007-10-18 22:05 ` Benjamin Herrenschmidt
2007-10-18 22:05 ` Benjamin Herrenschmidt
2007-10-18 22:52 ` Linus Torvalds
2007-10-18 22:52 ` Linus Torvalds
2007-10-18 23:17 ` Benjamin Herrenschmidt
2007-10-18 23:17 ` Benjamin Herrenschmidt
2007-10-18 23:39 ` Linus Torvalds
2007-10-18 23:39 ` Linus Torvalds
2007-10-18 23:52 ` Benjamin Herrenschmidt
2007-10-18 23:52 ` Benjamin Herrenschmidt
2007-10-19 2:32 ` Herbert Xu
2007-10-19 2:32 ` Herbert Xu
2007-10-19 2:52 ` Nick Piggin
2007-10-19 2:52 ` Nick Piggin
2007-10-19 3:28 ` Herbert Xu
2007-10-19 3:28 ` Herbert Xu
2007-10-19 4:49 ` Nick Piggin
2007-10-19 4:49 ` Nick Piggin
2007-10-19 2:55 ` Linus Torvalds
2007-10-19 2:55 ` Linus Torvalds
2007-10-19 3:26 ` Linus Torvalds
2007-10-19 3:26 ` Linus Torvalds
2007-10-19 4:11 ` Benjamin Herrenschmidt
2007-10-19 4:11 ` Benjamin Herrenschmidt
2007-10-19 4:26 ` Benjamin Herrenschmidt
2007-10-19 4:26 ` Benjamin Herrenschmidt
2007-10-19 5:53 ` Herbert Xu
2007-10-19 5:53 ` Herbert Xu
2007-10-19 4:20 ` Herbert Xu
2007-10-19 4:20 ` Herbert Xu
2007-10-19 4:29 ` Benjamin Herrenschmidt [this message]
2007-10-19 4:29 ` Benjamin Herrenschmidt
2007-10-19 4:35 ` Benjamin Herrenschmidt
2007-10-19 4:35 ` Benjamin Herrenschmidt
2007-10-19 4:48 ` Herbert Xu
2007-10-19 4:48 ` Herbert Xu
2007-10-19 4:58 ` Benjamin Herrenschmidt
2007-10-19 4:58 ` Benjamin Herrenschmidt
2007-10-21 21:10 ` Benjamin Herrenschmidt
2007-10-21 21:10 ` Benjamin Herrenschmidt
2007-10-23 3:26 ` [IRQ]: Fix synchronize_irq races with IRQ handler Herbert Xu
2007-10-23 3:26 ` Herbert Xu
2007-10-19 5:36 ` [NET]: Fix possible dev_deactivate race condition Herbert Xu
2007-10-19 5:36 ` Herbert Xu
2007-10-19 5:38 ` David Miller
2007-10-19 5:38 ` David Miller
2007-10-19 7:35 ` Peter Zijlstra
2007-10-19 7:35 ` Peter Zijlstra
2007-10-19 9:29 ` Herbert Xu
2007-10-19 9:29 ` Herbert Xu
2007-10-18 14:35 ` [PATCH] synchronize_irq needs a barrier Herbert Xu
2007-10-18 14:35 ` Herbert Xu
2007-10-18 21:35 ` Benjamin Herrenschmidt
2007-10-18 21:35 ` Benjamin Herrenschmidt
2007-10-20 2:02 ` Maxim Levitsky
2007-10-20 2:02 ` Maxim Levitsky
2007-10-20 2:25 ` Linus Torvalds
2007-10-20 2:25 ` Linus Torvalds
2007-10-20 3:10 ` Maxim Levitsky
2007-10-20 3:10 ` Maxim Levitsky
2007-10-20 4:06 ` Benjamin Herrenschmidt
2007-10-20 4:06 ` Benjamin Herrenschmidt
2007-10-20 4:04 ` Benjamin Herrenschmidt
2007-10-20 4:04 ` Benjamin Herrenschmidt
2007-10-20 4:09 ` Benjamin Herrenschmidt
2007-10-20 4:09 ` Benjamin Herrenschmidt
2007-10-20 3:37 ` Herbert Xu
2007-10-20 3:37 ` Herbert Xu
2007-10-20 3:56 ` Benjamin Herrenschmidt
2007-10-20 3:56 ` Benjamin Herrenschmidt
2007-10-20 4:24 ` Maxim Levitsky
2007-10-20 4:24 ` Maxim Levitsky
2007-10-20 5:04 ` Benjamin Herrenschmidt
2007-10-20 5:04 ` Benjamin Herrenschmidt
2007-10-20 5:36 ` Maxim Levitsky
2007-10-20 5:36 ` Maxim Levitsky
2007-10-20 5:46 ` Benjamin Herrenschmidt
2007-10-20 5:46 ` Benjamin Herrenschmidt
2007-10-20 6:06 ` Maxim Levitsky
2007-10-20 6:06 ` Maxim Levitsky
2007-10-20 6:13 ` Benjamin Herrenschmidt
2007-10-20 6:13 ` Benjamin Herrenschmidt
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