scsi: ibmvfc: Fix command state accounting and stale response detection

Prior to commit 1f4a4a19508d ("scsi: ibmvfc: Complete commands outside the
host/queue lock") responses to commands were completed sequentially with
the host lock held such that a command had a basic binary state of active
or free. It was therefore a simple affair of ensuring the assocaiated
ibmvfc_event to a VIOS response was valid by testing that it was not
already free. The lock relexation work to complete commands outside the
lock inadverdently made it a trinary command state such that a command is
either in flight, received and being completed, or completed and now
free. This breaks the stale command detection logic as a command may be
still marked active and been placed on the delayed completion list when a
second stale response for the same command arrives. This can lead to double
completions and list corruption. This issue was exposed by a recent VIOS
regression were a missing memory barrier could occasionally result in the
ibmvfc client receiving a duplicate response for the same command.

Fix the issue by introducing the atomic ibmvfc_event.active to track the
trinary state of a command. The state is explicitly set to 1 when a command
is successfully sent. The CRQ response handlers use
atomic_dec_if_positive() to test for stale responses and correctly
transition to the completion state when a active command is received.
Finally, atomic_dec_and_test() is used to sanity check transistions when
commands are freed as a result of a completion, or moved to the purge list
as a result of error handling or adapter reset.

Link: https://lore.kernel.org/r/20210716205220.1101150-1-tyreld@linux.ibm.com
Fixes: 1f4a4a19508d ("scsi: ibmvfc: Complete commands outside the host/queue lock")
Cc: stable@vger.kernel.org
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/scsi/ibmvscsi/ibmvfc.h b/drivers/scsi/ibmvscsi/ibmvfc.h
index 4f0f3baefae4..92fb889d7eb0 100644
--- a/drivers/scsi/ibmvscsi/ibmvfc.h
+++ b/drivers/scsi/ibmvscsi/ibmvfc.h
@@ -745,6 +745,7 @@ struct ibmvfc_event {
 	struct ibmvfc_target *tgt;
 	struct scsi_cmnd *cmnd;
 	atomic_t free;
+	atomic_t active;
 	union ibmvfc_iu *xfer_iu;
 	void (*done)(struct ibmvfc_event *evt);
 	void (*_done)(struct ibmvfc_event *evt);