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

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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
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