Don't return from the abort request until the target command is complete.
Mark outstanding commands which have a pending abort, and do not send them
to the host if we can avoid it.

If the current command has been aborted, do not call the SCSI command
completion routine from the I/O path: when the abort returns successfully,
the SCSI mid-layer will handle the completion implicitly.

The following race was possible in theory.

1. LLD is requested to abort a scsi command
2. scsi command completes
3. The struct CommandList associated with 2 is made available.
4. new io request to LLD to another LUN re-uses struct CommandList
5. abort handler follows scsi_cmnd->host_scribble and
   finds struct CommandList and tries to aborts it.

Now we have aborted the wrong command.

Fix by resetting the scsi_cmd field of struct CommandList
upon completion and making the abort handler check that
the scsi_cmd pointer in the CommadList struct matches the
scsi_cmnd that it has been asked to abort.
Reviewed-by: NScott Teel <scott.teel@pmcs.com>
Reviewed-by: NKevin Barnett <kevin.barnett@pmcs.com>
Reviewed-by: NTomas Henzl <thenzl@redhat.com>
Reviewed-by: NHannes Reinecke <hare@Suse.de>
Signed-off-by: NWebb Scales <webbnh@hp.com>
Signed-off-by: NDon Brace <don.brace@pmcs.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJames Bottomley <JBottomley@Odin.com>