When doing the following test steps, an error was found:
  step 1: modprobe 9pnet_virtio succeeded
    # modprobe 9pnet_virtio      <-- OK

  step 2: fault injection in sysfs_create_file()
    # modprobe -r 9pnet_virtio   <-- OK
    # ...
      FAULT_INJECTION: forcing a failure.
      name failslab, interval 1, probability 0, space 0, times 0
      CPU: 0 PID: 3790 Comm: modprobe Tainted: G        W
      6.1.0-rc6-00285-g6a1e40c4b995-dirty #108
      Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
      Call Trace:
       <TASK>
       ...
       should_failslab+0xa/0x20
       ...
       sysfs_create_file_ns+0x130/0x1d0
       p9_virtio_probe+0x662/0xb30 [9pnet_virtio]
       virtio_dev_probe+0x608/0xae0
       ...
       </TASK>
      9pnet_virtio: probe of virtio3 failed with error -12

  step 3: modprobe virtio_net failed
    # modprobe 9pnet_virtio       <-- failed
      9pnet_virtio: probe of virtio3 failed with error -2

The root cause of the problem is that the virtqueues are not
stopped on the error handling path when sysfs_create_file()
fails in p9_virtio_probe(), resulting in an error "-ENOENT"
returned in the next modprobe call in setup_vq().

virtio_pci_modern_device uses virtqueues to send or
receive message, and "queue_enable" records whether the
queues are available. In vp_modern_find_vqs(), all queues
will be selected and activated, but once queues are enabled
there is no way to go back except reset.

Fix it by reset virtio device on error handling path. After
virtio_find_single_vq() succeeded, all virtqueues should be
stopped on error handling path.

Fixes: 1fcf0512c9c8 ("virtio_pci: modern driver")
Signed-off-by: Li Zetao <lizetao1@huawei.com>
---
 net/9p/trans_virtio.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index e757f0601304..39933187284b 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -668,6 +668,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
 out_free_tag:
 	kfree(tag);
 out_free_vq:
+	virtio_reset_device(vdev);
 	vdev->config->del_vqs(vdev);
 out_free_chan:
 	kfree(chan);
-- 
2.25.1

On Monday, November 28, 2022 3:10:02 AM CET Li Zetao wrote:
> When doing the following test steps, an error was found:
>   step 1: modprobe 9pnet_virtio succeeded
>     # modprobe 9pnet_virtio      <-- OK
> 
>   step 2: fault injection in sysfs_create_file()
>     # modprobe -r 9pnet_virtio   <-- OK
>     # ...
>       FAULT_INJECTION: forcing a failure.
>       name failslab, interval 1, probability 0, space 0, times 0
>       CPU: 0 PID: 3790 Comm: modprobe Tainted: G        W
>       6.1.0-rc6-00285-g6a1e40c4b995-dirty #108
>       Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
>       Call Trace:
>        <TASK>
>        ...
>        should_failslab+0xa/0x20
>        ...
>        sysfs_create_file_ns+0x130/0x1d0
>        p9_virtio_probe+0x662/0xb30 [9pnet_virtio]
>        virtio_dev_probe+0x608/0xae0
>        ...
>        </TASK>
>       9pnet_virtio: probe of virtio3 failed with error -12
> 
>   step 3: modprobe virtio_net failed
>     # modprobe 9pnet_virtio       <-- failed
>       9pnet_virtio: probe of virtio3 failed with error -2
> 
> The root cause of the problem is that the virtqueues are not
> stopped on the error handling path when sysfs_create_file()
> fails in p9_virtio_probe(), resulting in an error "-ENOENT"
> returned in the next modprobe call in setup_vq().
> 
> virtio_pci_modern_device uses virtqueues to send or
> receive message, and "queue_enable" records whether the
> queues are available. In vp_modern_find_vqs(), all queues
> will be selected and activated, but once queues are enabled
> there is no way to go back except reset.
> 
> Fix it by reset virtio device on error handling path. After
> virtio_find_single_vq() succeeded, all virtqueues should be
> stopped on error handling path.
> 
> Fixes: 1fcf0512c9c8 ("virtio_pci: modern driver")
> Signed-off-by: Li Zetao <lizetao1@huawei.com>
> ---

As others said, comment should probably be adjusted, apart from that:

Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>

>  net/9p/trans_virtio.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index e757f0601304..39933187284b 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -668,6 +668,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
>  out_free_tag:
>  	kfree(tag);
>  out_free_vq:
> +	virtio_reset_device(vdev);
>  	vdev->config->del_vqs(vdev);
>  out_free_chan:
>  	kfree(chan);
>