On Mon, 13 Jan 2020, Oliver Neukum wrote: > Am Sonntag, den 12.01.2020, 19:30 -0800 schrieb EJ Hsu: > > Hi, > > first, thank you for diagnosing this unusual bug. > > > When a uas disk is plugged into an external hub, uas_probe() > > will be called by the hub thread to do the probe. It will > > first create a SCSI host and then do the scan for this host. > > During the scan, it will probe the LUN using SCSI INQUERY command > > which will be packed in the URB and submitted to uas disk. > > > > There might be a chance that this external hub with uas disk > > attached is unplugged during the scan. In this case, uas driver > > will fail to submit the URB (due to the NOTATTACHED state of uas > > device) and try to put this SCSI command back to request queue > > waiting for next chance to run. > > Isn't that the bug? A command to a detached device should fail. > Could you please elaborate? This issue would not be limited to uas. > It is not enough to do this in disconnect() > We are guarded against runtime PM, but not against system sleep. > You'd need to handle this in suspend() and resume(), too. > And, unfortunately, the device could be reset from another interface. This is more or less a copy of the way usb-storage works. That driver doesn't have any protection here against suspend/resume or reset, and it's not clear that any such protection is needed. > Is this approach really necessary? It solves the problem, but > if you want to get it right, the corner cases are ugly. Minimizing the amount of time spent running in the context of the hub thread is generally a good thing to do. Alan Stern
