This patch fixes a hang that can occur in ATA EH with ipr. With ipr's
usage of libata, commands should never end up on ap->eh_done_q. The
timeout function we use for ipr, even for SATA devices, is
scsi_times_out, so ATA_QCFLAG_EH_SCHEDULED never gets set for ipr and EH
is driven completely by ipr and SCSI. The SCSI EH thread ends up calling
ipr's eh_device_reset_handler, which then calls
ata_std_error_handler. This ends up calling ipr_sata_reset, which issues
a reset to the device. This should result in all pending commands
getting failed back and having ata_qc_complete called for them, which
should end up clearing ATA_QCFLAG_FAILED as qc->flags gets zeroed in
ata_qc_free.  This ensures that when we end up in ata_eh_finish, we
don't do anything more with the command.

On adapters that only support a single interrupt and when running with
two MSI-X vectors or less, the adapter firmware guarantees that
responses to all outstanding commands are sent back prior to sending the
response to the SATA reset command.  On newer adapters supporting
multiple HRRQs, however, this can no longer be guaranteed, since the
command responses and reset response may be processed on different
HRRQs.

If ipr returns from ipr_sata_reset before the outstanding command was
returned, this sends us down the path of __ata_eh_qc_complete which then
moves the associated scsi_cmd from the work_q in
scsi_eh_bus_device_reset to ap->eh_done_q, which then will sit there
forever and we will be wedged.

This patch fixes this up by ensuring that any outstanding commands are
flushed before returning from eh_device_reset_handler for a SATA device.
Reported-by: David Jeffery <djeffery@redhat.com>
Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Reviewed-by: Wendy Xiong <wenxiong@linux.vnet.ibm.com>
Tested-by: Wendy Xiong <wenxiong@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>