Re: [PATCH] vhost-scsi: do not relock event vq mutex on send_evt fallback

[Mike Christie <michael.christie@oracle.com>]

On 9/12/26 4:04 AM, Jia Jia wrote:
> vhost_scsi_send_evt() is called with the event virtqueue mutex held.
> If the worker is gone, the fallback currently calls
> vhost_scsi_complete_events(), which tries to acquire the same mutex again
> and deadlocks the caller.
> 
> Split event completion into a helper for callers that already hold the
> mutex and a locking wrapper for the event worker. Use the helper on the
> fallback path.
> 
> Link: https://lore.kernel.org/all/20260905005352.1E5B01F00A3D@smtp.kernel.org/
> Fixes: b1b2ce58ed23 ("vhost-scsi: Handle vhost_vq_work_queue failures for events")
> Signed-off-by: Jia Jia <physicalmtea@gmail.com>
> ---
> Sashiko AI flagged this while reviewing
> the vhost-scsi event queue fix.
> This is a pre-existing self-deadlock. It was reproduced in a follow-up test.
> 
> Trigger: vq->worker == NULL. vhost_vq_work_queue() then returns false,
> and a subsequent vhost_scsi_do_plug() call deadlocks. I do not know what
> normal condition gets us here; the normal vhost-scsi worker detach/reset
> paths do not reach this code. The only reproduction I could come up with
> was killing the vhost-scsi worker. This still looks like a low-probability
> condition.

Reviewed-by: Mike Christie <michael.christie@oracle.com>