tree c7f5c430603383d0875633f983d0c21030b8d715
parent d6d211db37e75de2ddc3a4f979038c40df7cc79c
author Mikulas Patocka <mpatocka@redhat.com> 1399578697 -0400
committer James Hogan <james.hogan@imgtec.com> 1400108434 +0100

metag: fix memory barriers

Volatile access doesn't really imply the compiler barrier. Volatile access
is only ordered with respect to other volatile accesses, it isn't ordered
with respect to general memory accesses. Gcc may reorder memory accesses
around volatile access, as we can see in this simple example (if we
compile it with optimization, both increments of *b will be collapsed to
just one):

void fn(volatile int *a, long *b)
{
	(*b)++;
	*a = 10;
	(*b)++;
}

Consequently, we need the compiler barrier after a write to the volatile
variable, to make sure that the compiler doesn't reorder the volatile
write with something else.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: James Hogan <james.hogan@imgtec.com>