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From: Chris Snook <>
To: KOSAKI Motohiro <>
Cc: Huang Ying <>,
	Andrew Morton <>,
	"" <>
Subject: Re: [PATH -mm -v2] Fix a race condtion of oops_in_progress
Date: Mon, 10 Nov 2008 13:45:00 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

KOSAKI Motohiro wrote:
>>>> As far as I know, barriers don't cause changes to be visible on other
>>>> CPUs faster too. It just guarantees corresponding operations after will
>>>> not get executed until that before have finished. And, I don't think we
>>>> need make changes to be visible on other CPUs faster.
>>> You're correct that barrier() has no impact on other CPUs.  wmb() and rmb() do. 
>>>   If we don't need to make changes visible any faster, what's the point in using 
>>> atomic_set()?  It's not any less racy.  atomic_inc() and atomic_dec() would be 
>>> less racy, but you're not using those.
>> In default bust_spinlocks() implementation in lib/bust_spinlocks.c,
>> atomic_inc() and atomic_dec_and_test() is used. Which is used by x86
>> too. In some other architecture, atomic_set() is used to replace
>> "oops_in_progress = <xxx>". So this patch fixes architectures which use
>> default bust_spinlocks(), other architectures can be fixed by
>> corresponding architecture developers.
> I think Chris is right.
> So, I reccomend to read Documentation/memory-barriers.txt
> Almost architecture gurantee atomic_inc cause barrier implicitly.
> but not _all_ architecture.

The rmb() before atomic_read() is even more critical, since that's a 
non-barrier operation on nearly all platforms.

-- Chris

  reply	other threads:[~2008-11-10 18:45 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-29  8:26 Huang Ying
2008-10-29  8:34 ` Ingo Molnar
2008-10-29  8:42   ` Huang Ying
2008-10-29 14:51 ` Chris Snook
2008-10-30  2:02   ` Huang Ying
2008-10-31 16:42     ` Chris Snook
2008-11-03  1:52       ` Huang Ying
2008-11-03 18:44         ` Chris Snook
2008-11-04  1:41           ` Huang Ying
2008-11-10  7:35             ` KOSAKI Motohiro
2008-11-10 18:45               ` Chris Snook [this message]
2008-11-11  1:05               ` Huang Ying
2008-11-11  1:10                 ` Chris Snook
2008-11-11  1:19                   ` Huang Ying

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