Ejecting removable disk causes a flood of ALLOW_MEDIUM_REMOVAL

[Albert Lee <albertcc@tw.ibm.com>]

Hi Doug,

A problem related to SG_IO.
When testing the 2.6.18-rc1 libata, a flood of ALLOW_MEDIUM_REMOVAL is seen
after ejecting a removable disk drive:

http://bugzilla.kernel.org/show_bug.cgi?id=6799

The interaction to trigger the problem is below:
1. The "eject" utility, using SG_IO, issues ALLOW_MEDIUM_REMOVAL twice to unlock the disk of the device.
2. The disk of the physical device is now unlocked, however, sdev->locked is still 1, inconsistent with the physical device status.
3. The "eject" utility ejects the disk by START_STOP_UNIT.
4. Someone issues TEST_UNIT_READY. The device is not ready since no disk inside. ATAPI check condition returned.
5. 2.6.18-rc1 libata EH triggered in SCSI EH context to request sense.
6. scsi_restart_operations(), seeing sdev->locked == 1, tries to lock the door.
7. Lock failed since no disk inside. ATAPI check condition returned.
8. 2.6.18 libata EH triggered in SCSI EH context. Goto 5 and loop forever until the disk is inserted again.

It looks more like eject/scsi problem. (Libata 2.6.17 EH is not affected by the problem 
because the request sense is done when qc is completed, not in the SCSI EH context.)

Maybe adding a filter to the SCSI SG IO layer to
 - Check incoming SCSI commands
 - Whenever ALLOW_MEDIUM_REMOVAL is seen, update the sdev->locked to make the 
   kernel data structure consistent with the physical device status
can fix the problem?

--
albert