vhost: Fix worker hangs due to missed wake up calls

We can race where we have added work to the work_list, but
vhost_task_fn has passed that check but not yet set us into
TASK_INTERRUPTIBLE. wake_up_process will see us in TASK_RUNNING and
just return.

This bug was intoduced in commit f9010dbdce91 ("fork, vhost: Use
CLONE_THREAD to fix freezer/ps regression") when I moved the setting
of TASK_INTERRUPTIBLE to simplfy the code and avoid get_signal from
logging warnings about being in the wrong state. This moves the setting
of TASK_INTERRUPTIBLE back to before we test if we need to stop the
task to avoid a possible race there as well. We then have vhost_worker
set TASK_RUNNING if it finds work similar to before.

Fixes: f9010dbdce91 ("fork, vhost: Use CLONE_THREAD to fix freezer/ps regression")
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Message-Id: <20230607192338.6041-3-michael.christie@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index ca1041c..1f80eac 100644 (file)
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -341,6 +341,8 @@ static bool vhost_worker(void *data)
 
        node = llist_del_all(&worker->work_list);
        if (node) {
+               __set_current_state(TASK_RUNNING);
+
                node = llist_reverse_order(node);
                /* make sure flag is seen after deletion */
                smp_wmb();

diff --git a/kernel/vhost_task.c b/kernel/vhost_task.c
index f80d5c5..da35e5b 100644 (file)
--- a/kernel/vhost_task.c
+++ b/kernel/vhost_task.c
@@ -28,10 +28,6 @@ static int vhost_task_fn(void *data)
        for (;;) {
                bool did_work;
 
-               /* mb paired w/ vhost_task_stop */
-               if (test_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags))
-                       break;
-
                if (!dead && signal_pending(current)) {
                        struct ksignal ksig;
                        /*
@@ -48,11 +44,17 @@ static int vhost_task_fn(void *data)
                                clear_thread_flag(TIF_SIGPENDING);
                }
 
+               /* mb paired w/ vhost_task_stop */
+               set_current_state(TASK_INTERRUPTIBLE);
+
+               if (test_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags)) {
+                       __set_current_state(TASK_RUNNING);
+                       break;
+               }
+
                did_work = vtsk->fn(vtsk->data);
-               if (!did_work) {
-                       set_current_state(TASK_INTERRUPTIBLE);
+               if (!did_work)
                        schedule();
-               }
        }
 
        complete(&vtsk->exited);