xen-netback: fix race between napi_complete() and interrupt handler

When the NAPI budget was not all used, xenvif_poll() would call
napi_complete() /after/ enabling the interrupt.  This resulted in a
race between the napi_complete() and the napi_schedule() in the
interrupt handler.  The use of local_irq_save/restore() avoided by
race iff the handler is running on the same CPU but not if it was
running on a different CPU.

Fix this properly by calling napi_complete() before reenabling
interrupts (in the xenvif_napi_schedule_or_enable_irq() call).

Signed-off-by: David Vrabel <[email protected]>
Acked-by: Wei Liu <[email protected]>
Acked-by: Ian Campbell <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
3 files changed