On Tue, 2008-05-20 at 15:53 -0700, David Miller wrote:From: Scott Wood <scottwood@xxxxxxxxxxxxx>
Date: Tue, 20 May 2008 17:43:58 -0500
David Miller wrote:The __volatile__ in the asm construct disallows movement of the
inline asm relative to statements surrounding it.
The only reason barrier() in kernel.h needs a memory clobber is
because of a bug in ancient versions of gcc. In fact, I think
that memory clobber might even be removable.
Current versions of GCC seem quite happy to move non-asm memory accesses
around a volatile asm without a memory clobber; see the test Trent posted.
Indeed, and even the GCC manual is clear about this.
So what is the scope of that problem ?
IE. Take an x86 version of that test, writing to memory, doing a writel
to some MMIO, then another memory write, can those be re-ordered with
the current x86 version of writel ?