On Wed, 15 Aug 2007, Paul E. McKenney wrote:
> 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.
Yup, I've just verified this with a testcase. So a call to any function
outside of the current compilation unit acts as a compiler barrier. Cool.
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