tree d62e7dcc09dddd0edc6d507e7b219c16e66d3b02
parent 6e5aa7efb27aec7e55b6463fa2c8db594c4226fa
author Rusty Russell <rusty@rustcorp.com.au> 1202187004 -0500
committer Rusty Russell <rusty@rustcorp.com.au> 1202129404 +1100

virtio: handle interrupts after callbacks turned off

Anthony Liguori found double interrupt suppression in the virtio_net
driver, triggered by two skb_recv_done's in a row.  This is because
virtio_ring's interrupt suppression is a best-effort optimization: it
contains no synchronization so the host can miss it and still send
interrupts.

But it's certainly nicer for virtio users if calling disable_cb
actually disables callbacks, so we check for the race in the interrupt
routine.

Note: SMP guests might require syncronization here, but since
disable_cb is actually called from interrupt context, there has to be
some form of synchronization before the next same interrupt handler is
called (Linux guarantees that the same device's irq handler will never
run simultanously on multiple CPUs).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>