RE: [Xen-devel] Re: [PATCH] Fix cpu offline bug

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 08.03.11 at 10:47, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
> Jan, I'm not quite clear your meaning.
> Why and where need to insert barrier, or volatile cpu_state?
 
     while ( (seen_state = cpu_state) != CPU_STATE_DEAD )
     {
+        barrier();
         BUG_ON(seen_state != CPU_STATE_DYING);
         mdelay(100);
         cpu_relax();

Without this, the compiler is free to eliminate "seen_state" in favor
of reading "cpu_state" twice (irrespective of the optimizer very
likely trying to do exactly the opposite).

Jan


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