The hardware must not see that is given ownership of a buffer until it
is
completely written, and when the driver receives ownership of a buffer,
it must ensure that any other reads to the buffer reflect its final
state. Thus, I/O barriers are added where required.
Without this patch, I have observed GCC reordering the setting of
bdp->length and bdp->status in gfar_new_skb.
The :::"memory" in the barriers you used prevent GCC
from reordering accesses around the barriers.
AFAICS you need stronger barriers though; {w,r,}mb(),
to prevent _any_ reordering of those memory accesses,
not just the compiler-generated ones.
Segher
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