From: David Daney <ddaney@caviumnetworks.com>
To: rostedt@goodmis.org
Cc: LKML <linux-kernel@vger.kernel.org>,
kernel-janitors <kernel-janitors@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-arch@vger.kernel.org, Greg KH <greg@kroah.com>,
Andy Whitcroft <apw@canonical.com>,
Ralf Baechle <ralf@linux-mips.org>,
linux-mips <linux-mips@linux-mips.org>
Subject: Re: Lots of bugs with current->state = TASK_*INTERRUPTIBLE
Date: Thu, 21 Jan 2010 12:21:45 -0800 [thread overview]
Message-ID: <4B58B759.8000002@caviumnetworks.com> (raw)
In-Reply-To: <1264105104.31321.298.camel@gandalf.stny.rr.com>
>>
>> This is what I thought.
>>
>> My cpu (Cavium Octeon) does not have out of order reads, so my wmb() is
>
> Can you have reads that are out of order wrt writes? Because the above
> does not have out of order reads. It just had a read that came before a
> write. The above code could look like:
>
> (hypothetical assembly language)
>
> ld r2, TASK_UNINTERRUPTIBLE
> st r2, (current->state)
> wmb
> ld r1, (x)
> cmp r1, 0
>
> Is it possible for the CPU to do the load of r1 before storing r2? If
> so, then the bug still exists.
>
Indeed it is. Lockless operations make my head hurt.
Thanks for clarifying.
David Daney
> -- Steve
>
>
>> in fact a full mb() from the point of view of the current CPU. So I
>> think I could weaken my bariers in set_current_state() and still get
>> correct operation. However as you say...
>>
>
>
>
prev parent reply other threads:[~2010-01-21 20:21 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-19 20:29 Lots of bugs with current->state = TASK_*INTERRUPTIBLE Steven Rostedt
2010-01-19 20:58 ` Julia Lawall
2010-01-19 20:58 ` Julia Lawall
2010-01-19 21:08 ` Steven Rostedt
2010-01-21 10:47 ` Julia Lawall
2010-01-21 10:47 ` Julia Lawall
2010-01-21 10:53 ` Frederic Weisbecker
2010-01-21 10:56 ` Peter Zijlstra
2010-01-21 10:59 ` Frederic Weisbecker
2010-01-21 17:31 ` Steven Rostedt
2010-01-21 17:31 ` Steven Rostedt
2010-01-21 18:12 ` Julia Lawall
2010-01-21 19:18 ` David Daney
2010-01-21 19:34 ` Steven Rostedt
2010-01-21 19:57 ` David Daney
2010-01-21 20:18 ` Steven Rostedt
2010-01-21 20:18 ` Steven Rostedt
2010-01-21 20:21 ` David Daney [this message]
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