On Thu, Dec 12, 2013 at 05:04:31PM -0500, Alan Stern wrote: > 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. Thanks for looking into this. I think just getting rid of the WARN would be sufficient. Can you make a patch for that? The patch still won't help with the UAS issues with scsi_init_shared_tag_map though. Sarah Sharp -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
