Re: [usb-storage] UAS hangs khubd on USB disconnect

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 12/13/2013 09:03 PM, James Bottomley wrote:

<snip>

> Actually, I think I have this figured out.  There's a thinko in one of
> the scsi_target_reap() cases.  The original (and still existing) problem
> with targets is that nothing creates them and nothing destroys them, so,
> while we could rely on the refcounting of the device model to preserve
> the actual target object, we had no idea when to remove it from
> visibility.  That was the job of the reap reference, to track
> visibility.  It looks like the reap on device last put is occurring too
> late.  I think we should reap immediately after doing the sdev
> device_del, so does this fix the warn on? (I'm not sure because no-one
> has actually posted a backtrace, but it sounds like this is the
> problem).
>
> James
>
> ---
>
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index 8ff62c2..98d4eb3 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -399,8 +399,6 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
>   	/* NULL queue means the device can't be used */
>   	sdev->request_queue = NULL;
>
> -	scsi_target_reap(scsi_target(sdev));
> -
>   	kfree(sdev->inquiry);
>   	kfree(sdev);
>
> @@ -1044,6 +1042,8 @@ void __scsi_remove_device(struct scsi_device *sdev)
>   	} else
>   		put_device(&sdev->sdev_dev);
>
> +	scsi_target_reap(scsi_target(sdev));
> +
>   	/*
>   	 * Stop accepting new requests and wait until all queuecommand() and
>   	 * scsi_run_queue() invocations have finished before tearing down the

I've given this patch a try and it fixes the blk-tag.c: 89 BUG() I was seeing.

As for the other patch you (James) have send for that problem:

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 8ff62c2..98d4eb3 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -399,8 +399,6 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
  	/* NULL queue means the device can't be used */
  	sdev->request_queue = NULL;

-	scsi_target_reap(scsi_target(sdev));
-
  	kfree(sdev->inquiry);
  	kfree(sdev);

@@ -1044,6 +1042,8 @@ void __scsi_remove_device(struct scsi_device *sdev)
  	} else
  		put_device(&sdev->sdev_dev);

+	scsi_target_reap(scsi_target(sdev));
+
  	/*
  	 * Stop accepting new requests and wait until all queuecommand() and
  	 * scsi_run_queue() invocations have finished before tearing down the

That too fixes the blk-tag.c: 89 BUG() I was seeing. Either patch by itself
seems to be enough to fix this issue for me.

Thanks & Regards,

Hans