[BUG] 2.4.21-pre3 hdparm -X violates IDE locking

[Ross Biro]

This bug impacts all versions of the kernel that I have looked at 
including 2.4.18 and above.  It probably impacts many other versions as 
well.

hdparm -X issues a drive command ioctl which eventually issue a command 
to the drive bypassing all of the normal locking.  The net effect is 
that a command can be set to the drive when the drive is not ready. 
 Some drives lock up when this happens.

The call chain is

ide_ioctl calls
ide_cmd_ioctl

If the command is a set features to change the communications speed, 
after the command is complete, ide_cmd_ioctl calls

ide_set_xfer_rate

ide_set_xfer_rate then calls drive->speedproc.

Most speedprocs then call ide_config_drive_speed
ide_config_drive_speed issue a set features command. and busy waits on it.

The easiest fix is to probably modify execute_drive_command to update 
drive->current_speed when it issues the appropriate SET FEATURES 
command, and then have ide_config_drive_speed do nothing if speed == 
current_speed.

I did a much bigger modification that handles changing drive speed 
specially and immediately.  I'll make patches for either one, but I 
wanted to get some opinions before I did so.

    Ross