On Wed, Aug 15, 2007 at 06:09:35PM +0200, Stefan Richter wrote:
> Herbert Xu wrote:
> > On Wed, Aug 15, 2007 at 08:05:38PM +0530, Satyam Sharma wrote:
> >>> I don't know if this here is affected:
>
> [...something like]
> b = atomic_read(a);
> for (i = 0; i < 4; i++) {
> msleep_interruptible(63);
> c = atomic_read(a);
> if (c != b) {
> b = c;
> i = 0;
> }
> }
>
> > Nope, we're calling schedule which is a rather heavy-weight
> > barrier.
>
> How does the compiler know that msleep() has got barrier()s?
Because msleep_interruptible() is in a separate compilation unit,
the compiler has to assume that it might modify any arbitrary global.
In many cases, the compiler also has to assume that msleep_interruptible()
might call back into a function in the current compilation unit, thus
possibly modifying global static variables.
Thanx, Paul
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