On Wed, 11 Dec 2013, Sarah Sharp wrote: > Hi Hans, > > I've been testing the UAS code you sent a pull request for against > 3.13-rc1, and I've run into a rather nasty issue with USB disconnect. > > I ran some tests with a USB 3.0 storage device under xHCI. The disk has > three 10GB partitions: ext3 (sdb1), ext4 (sdb2), and fat32 (sdb4). > There was a btrfs partition on sdb3, but I deleted it. > > If I start to play a movie on the ext4 partition, and then yank the USB > cable, the uas driver is unbound from the device. It looks like > something goes wrong in the SCSI layer shortly after that, causing an > oops in sysfs_remove_group(). I did a little testing. It turns out this WARN (not an oops) is the result of recent changes to sysfs, combined with the peculiar way the SCSI layer handles targets. In the new kernel, when you call device_del for some object, the object's directory and everything beneath it get removed from sysfs. This wasn't true in the past. When a USB drive is unplugged, almost everything below it gets unregistered. But not the SCSI target -- it remains registered until the number of "reap references" drops to 0. This doesn't happen until all the devices beneath it are released, which happens when all the open file references are closed and the filesystem is unmounted. So scsi_target_reap_usercontext ends up calling device_del for the target after everything else has been removed from sysfs. As part of normal device_del processing, attribute groups get removed. In particular the power/ subdirectory is removed from the target's sysfs directory. But the sysfs directories are long gone by this time, so sysfs_remove_group complains that it was asked to remove a non-existent subdirectory. Given the way things work now, I suspect these warnings are truly harmless. We could simply get rid of the WARN in sysfs_remove_group. The alternative is to call device_del for SCSI targets earlier on, such as when their hosts are unregistered. I don't know how James would feel about this approach. It would be difficult because targets use their own reference counts instead of relying on the usual device refcounting mechanism. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
