drivers/xen/pvcalls-back.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
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 <volodymyr_babchuk@epam.com>
Reported-by: Oleksii Moisieiev <oleksii_moisieiev@epam.com>
---
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
On 19.01.23 22:11, Volodymyr Babchuk wrote: > 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 <volodymyr_babchuk@epam.com> > Reported-by: Oleksii Moisieiev <oleksii_moisieiev@epam.com> Pushed to: xen/tip.git for-linus-6.3 Juergen
On 19.01.23 22:11, Volodymyr Babchuk wrote: > 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 <volodymyr_babchuk@epam.com> > Reported-by: Oleksii Moisieiev <oleksii_moisieiev@epam.com> Reviewed-by: Juergen Gross <jgross@suse.com> Juergen
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