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Date:      Mon, 08 Jul 2002 15:27:22 -0400 (EDT)
From:      John Baldwin <jhb@FreeBSD.org>
To:        David Xu <davidx@viasoft.com.cn>
Cc:        freebsd-current@FreeBSD.ORG, Julian Elischer <julian@elischer.org>
Subject:   RE: Timeout and SMP race
Message-ID:  <XFMail.20020708152722.jhb@FreeBSD.org>
In-Reply-To: <001101c222fa$9b32eed0$ef01a8c0@davidwnt>

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On 04-Jul-2002 David Xu wrote:
> while we are getting rid of Giant,  current race condition between softclock()
> and callout_stop() is unacceptable. the race causes two many places in source
> code would be modified to fit this new behaviour,  besides this, everywhere 
> callout_stop() is used need to hold sched_lock and do a mi_switch() and
> modify td_flags is also unacceptable, this SMP race should be resolved in 
> kern_timeout.c.

How would you resolve it while still preserving the existing semantics?
Saying "this race should be resolved" doesn't explain how you would go about
resolving it.  It's a lot harder than it looks.

-- 

John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/

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