Commit 4b13cbef authored Jun 07, 2023 by Mike Christie Committed by Michael S. Tsirkin Jun 08, 2023

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 f9010dbd ("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: f9010dbd ("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>

parent a284f09e

drivers/vhost/vhost.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -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();

kernel/vhost_task.c

+9 −7

Original line number	Diff line number	Diff line
		@@ -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);
		}

		did_work = vtsk->fn(vtsk->data);
		if (!did_work) {
		/* mb paired w/ vhost_task_stop */
		set_current_state(TASK_INTERRUPTIBLE);
		schedule();

		if (test_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags)) {
		__set_current_state(TASK_RUNNING);
		break;
		}

		did_work = vtsk->fn(vtsk->data);
		if (!did_work)
		schedule();
		}

		complete(&vtsk->exited);