ata: libata: Improve __ata_qc_complete()

The function __ata_qc_complete() is always called with a qc that already
has been dereferenced and so is guaranteed to be non-NULL (as otherwise
the kernel would have crashed). So remove the warning for a NULL qc as
it is useless.

Furthermore, the qc passed to __ata_qc_complete() must always be marked
as active with the ATA_QCFLAG_ACTIVE flag. If that is not the case, in
addition to the existing warning, return early so that we do not attempt
to complete an invalid qc.

Finally, fix the comment related to clearing the qc active flag as that
operation applies to all devices, not just ATAPI ones.
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>

drivers/ata/libata-core.c

@@ -4829,8 +4829,9 @@ void __ata_qc_complete(struct ata_queued_cmd *qc)
 	struct ata_port *ap;
 	struct ata_link *link;
 
-	WARN_ON_ONCE(qc == NULL); /* ata_qc_from_tag _might_ return NULL */
-	WARN_ON_ONCE(!(qc->flags & ATA_QCFLAG_ACTIVE));
+	if (WARN_ON_ONCE(!(qc->flags & ATA_QCFLAG_ACTIVE)))
+		return;
+
 	ap = qc->ap;
 	link = qc->dev->link;
 
@@ -4852,9 +4853,10 @@ void __ata_qc_complete(struct ata_queued_cmd *qc)
 		     ap->excl_link == link))
 		ap->excl_link = NULL;
 
-	/* atapi: mark qc as inactive to prevent the interrupt handler
-	 * from completing the command twice later, before the error handler
-	 * is called. (when rc != 0 and atapi request sense is needed)
+	/*
+	 * Mark qc as inactive to prevent the port interrupt handler from
+	 * completing the command twice later, before the error handler is
+	 * called.
 	 */
 	qc->flags &= ~ATA_QCFLAG_ACTIVE;
 	ap->qc_active &= ~(1ULL << qc->tag);