On Fri, 2008-05-23 at 13:14 -0700, Roland Dreier wrote:
> > + /* Tell compiler that status_blk fields can change. */
> > + barrier();
> > + if (status_idx != sblk->status_idx) {
>
> Is a compiler barrier sufficient here? It seems an out-of-order CPU
> could still mess things up, so an rmb() or smp_rmb() would be required.
>
The purpose of this compiler barrier is to make sure that the compiled
code will get the sblk->status_idx from memory which may change if the
chip DMAs a new status_idx.
This code is inside a while loop, so it is possible that the compiler
can optimize it to not load status_idx from memory.
Thanks.
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