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* [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked
@ 2021-06-06 13:29 Gautam Dawar
  2021-06-15 14:33 ` Jason Wang
  2021-07-03 19:01 ` gautam.dawar
  0 siblings, 2 replies; 5+ messages in thread
From: Gautam Dawar @ 2021-06-06 13:29 UTC (permalink / raw)
  Cc: martinh, hanand, gdawar, Michael S. Tsirkin, Jason Wang, kvm,
	virtualization, netdev, linux-kernel

From: Gautam Dawar <>

If some module invokes vdpa_device_unregister (usually in the module
unload function) when the userspace app (eg. QEMU) which had opened
the vhost-vdpa character device is still running, vhost_vdpa_remove()
function will block indefinitely in call to wait_for_completion().

This causes the vdpa_device_unregister caller to hang and with a
usual side-effect of rmmod command not returning when this call
is in the module_exit function.

This patch converts the wait_for_completion call to its timeout based
counterpart (wait_for_completion_timeout) and also adds a warning
message to alert the user/administrator about this hang situation.

To eventually fix this problem, a mechanism will be required to let
vhost-vdpa module inform the userspace of this situation and
userspace will close the descriptor of vhost-vdpa char device.
This will enable vhost-vdpa to continue with graceful clean-up.

Signed-off-by: Gautam Dawar <>
 drivers/vhost/vdpa.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index bfa4c6ef554e..572b64d09b06 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -1091,7 +1091,11 @@ static void vhost_vdpa_remove(struct vdpa_device *vdpa)
 		opened = atomic_cmpxchg(&v->opened, 0, 1);
 		if (!opened)
-		wait_for_completion(&v->completion);
+		wait_for_completion_timeout(&v->completion,
+					    msecs_to_jiffies(1000));
+		dev_warn_ratelimited(&v->dev,
+				     "%s waiting for /dev/%s to be closed\n",
+				     __func__, dev_name(&v->dev));
 	} while (1);

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2021-07-03 19:21 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-06-06 13:29 [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked Gautam Dawar
2021-06-15 14:33 ` Jason Wang
2021-07-03  8:11   ` Michael S. Tsirkin
2021-07-03 19:08     ` Gautam Dawar
2021-07-03 19:01 ` gautam.dawar

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