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 6:20
>>To: Zhang, Yanmin
>>Cc: linux-kernel@xxxxxxxxxxxxxxx; Pallipadi, Venkatesh; Shah, Rajesh
>>Subject: Re: [BUG] Variable stopmachine_state should be volatile
>>
>>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.

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