There is a sequence of events that can lead to a permanently masked event channel, because xen_irq_lateeoi() is newer called. This happens when a backend receives spurious write event from a frontend. In this case pvcalls_conn_back_write() returns early and it does not clears the map->write counter. As map->write > 0, pvcalls_back_ioworker() returns without calling xen_irq_lateeoi(). This leaves the event channel in masked state, a backend does not receive any new events from a frontend and the whole communication stops.
Move atomic_set(&map->write, 0) to the very beginning of pvcalls_conn_back_write() to fix this issue. Signed-off-by: Volodymyr Babchuk <[email protected]> Reported-by: Oleksii Moisieiev <[email protected]> --- drivers/xen/pvcalls-back.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c index a7d293fa8d14..60f5cd70d770 100644 --- a/drivers/xen/pvcalls-back.c +++ b/drivers/xen/pvcalls-back.c @@ -173,6 +173,8 @@ static bool pvcalls_conn_back_write(struct sock_mapping *map) RING_IDX cons, prod, size, array_size; int ret; + atomic_set(&map->write, 0); + cons = intf->out_cons; prod = intf->out_prod; /* read the indexes before dealing with the data */ @@ -197,7 +199,6 @@ static bool pvcalls_conn_back_write(struct sock_mapping *map) iov_iter_kvec(&msg.msg_iter, READ, vec, 2, size); } - atomic_set(&map->write, 0); ret = inet_sendmsg(map->sock, &msg, size); if (ret == -EAGAIN) { atomic_inc(&map->write); -- 2.38.1
