On Tue, 2012-10-30 at 16:34 +0100, Frederic Weisbecker wrote:
> Hi,
> And I still wonder if cpu_relax() is enough to prevent the compiler
> from correctly reloading work->flags in irq_work_sync() loop.
> Do we need ACCESS_ONCE()?
You mean this loop:
flags = work->flags & ~IRQ_WORK_PENDING;
for (;;) {
nflags = flags | IRQ_WORK_FLAGS;
oflags = cmpxchg(&work->flags, flags, nflags);
if (oflags == flags)
break;
if (oflags & IRQ_WORK_PENDING)
return false;
flags = oflags;
cpu_relax();
}
After the first loading of work->flags, you are worried about the
&work->flags in the cmpxchg()? The cmpxchg() will handle that itself. I
don't see any place that a ACCESS_ONCE() is required here. The cmpxchg()
acts on the address of work->flags, the compiler isn't involved with the
value at that address.
-- Steve
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