Re: [PATCH] scsi: core: Make SCSI host scan interruptible

[John Garry <john.garry@linux.dev>]

On 9/11/26 21:11, Bart Van Assche wrote:
> Writing to the sysfs "scan" attribute serializes SCSI host scans via
> shost->scan_mutex. In virtualized environments such as virtio-scsi with
> 256 target IDs, scanning non-existent targets repeatedly allocates and
> destroys temporary scsi_devices. Each iteration transitions the shared tag
> queue state and freezes request queues, causing a full bus scan to take
> tens of seconds.

So does this scan use all wildcard "- - -"?

> 
> When multiple processes initiate host scans concurrently, waiter tasks
> sleep in TASK_UNINTERRUPTIBLE on shost->scan_mutex. If the waiting tasks
> receive signals such as SIGKILL, they cannot wake up until the mutex is
> acquired, easily exceeding the hung task timeout and triggering
> khungtaskd warnings ("INFO: task hung in scsi_scan_host_selected").
> Furthermore, once a task finally acquires the mutex, it continues to
> perform the full scan even if a fatal signal is already pending.
> 
> Fix this by:
> 1. Use mutex_lock_interruptible() instead of mutex_lock() in
>     scsi_scan_host_selected(), allowing waiting tasks to sleep in
>     TASK_INTERRUPTIBLE and immediately wake up with -EINTR on signals.
> 2. Check signal_pending(current) in scsi_scan_host_selected(),
>     scsi_scan_channel(), __scsi_scan_target(), scsi_report_lun_scan(),
>     and scsi_sequential_lun_scan() to abort scanning early when a signal
>     is delivered.

If you want to be able to cancel a scan which is in progress, then why 
run it in the first place? I don't understand how this helps.