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If a command times out while we have deferred non-NCQ commands waiting to
be issued, the SCSI EH task is not immediately woken up as the waiting
deferred commands are never issued nor completed, thus leaving the SCSI
host in a busy state (shost->host_failed != scsi_host_busy(shost)) which
prevents the SCSI EH task from being woken up. Eventually, when the
deferred commands also time out, the SCSI EH task is woken up and the
timeout processing occurs.
Avoid this unnecessary SCSI EH task wake-up additional time by scheduling
a retry of all waiting deferred QCs, using the eh_timed_out SCSI host
template operation. The function ata_scsi_eh_timed_out() is introduced to
implement this operation.
However, terminating deferred commands with DID_REQUEUE to force a retry
by calling the function ata_scsi_requeue_deferred_qc() may still keep the
SCSI host in a busy state because the block layer may immediately re-issue
these commands. The solution to this is to schedule libata EH for the
port which suffered the command timeout to prevent accepting any new
command. ata_scsi_requeue_deferred_qc() is modified to add a call to
ata_port_schedule_eh() for this purpose.
In addition to this change, ata_scsi_requeue_deferred_qc() is also
modified to take a new timedout_scmd scsi command argument which indicates
the SCSI command that timed out. With this additional argument,
ata_scsi_requeue_deferred_qc() can now also terminate with DID_TIME_OUT
any timed out deferred qc, which simplifies ata_scsi_cmd_error_handler().
In this case, ata_scsi_requeue_deferred_qc() returns SCSI_EH_DONE, with
this return value propagated back to the ata_scsi_eh_timed_out() operation
to indicate to scsi_timeout() that the timed out command was handled and
no further processing is needed.
For non-timed out deferred qc that need to be retried,
ata_scsi_requeue_deferred_qc() returns SCSI_EH_NOT_HANDLED, thus
indicating to scsi_timeout() that the timed out command needs to go
through the SCSI EH (and libata EH) processing by adding it to the EH work
queue with scsi_eh_scmd_add().
One side effect of these changes is that the function atapi_qc_complete()
needs to be modified to ensure that a deferred ATAPI command that needs
to be retried is completed with DID_REQUEUE instead of the default
SAM_STAT_GOOD status, and a command that timed out is completed with
DID_TIME_OUT instead of SAM_STAT_CHECK_CONDITION.
Fixes: 0ea84089db ("ata: libata-scsi: avoid Non-NCQ command starvation")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Igor Pylypiv <ipylypiv@google.com>
Tested-by: Igor Pylypiv <ipylypiv@google.com>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
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