RE: [BUG] Variable stopmachine_state should be volatile

[Zhang, Yanmin]

>>-----Original Message-----
>>From: Pavel Machek [mailto:pavel@xxxxxx]
>>Sent: 2005年12月1日 11:26
>>To: Zhang, Yanmin
>>Cc: linux-kernel@xxxxxxxxxxxxxxx; Pallipadi, Venkatesh; Shah, Rajesh
>>Subject: Re: [BUG] Variable stopmachine_state should be volatile
>>
>>Hi!
>>
>>> >>Hi!
>>> >>
>>> >>> The model to access variable stopmachine_state is that a main thread
>>> >>> writes it and other threads read it. Its declaration has no sign
>>> >>> volatile. In the while loop in function stopmachine, this variable is
>>> >>> read, and compiler might optimize it by reading it once before the loop
>>> >>> and not reading it again in the loop, so the thread might enter dead
>>> >>> loop.
>>> >>
>>> >>No. volatile may look like a solution, but it usually is not. You may
>>> >>need some barriers, atomic_t or locking.
>>> >>								Pavel
>>> The original functions already use smp_mb/smp_wmb. My patch just
>>>tells compiler not to optimize by bringing the reading of
>>>stopmachine_state out of the while loop.
>>
>>Those barriers should already prevent compiler optimalization, no? If
>>they do not, just use some barriers that do.


I hit the problem when compiling 2.6 kernel by intel compiler.
How about to change the type of stopmachine_state to atomic_t?
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