scsi: fnic: Replace sgreset tag with max_tag_id

sgreset is issued with a SCSI command pointer. The device reset code
assumes that it was issued on a hardware queue, and calls block multiqueue
layer. However, the assumption is broken, and there is no hardware queue
associated with the sgreset, and this leads to a crash due to a null
pointer exception.

Fix the code to use the max_tag_id as a tag which does not overlap with the
other tags issued by mid layer.

Tested by running FC traffic for a few minutes, and by issuing sgreset on
the device in parallel. Without the fix, the crash is observed right away.
With this fix, no crash is observed.

Reviewed-by: Sesidhar Baddela <[e-mail]>
Tested-by: Karan Tilak Kumar <[e-mail]>
Signed-off-by: Karan Tilak Kumar <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/fnic/fnic.h

···
 
 #define DRV_NAME		"fnic"
 #define DRV_DESCRIPTION		"Cisco FCoE HBA Driver"
-#define DRV_VERSION		"1.6.0.54"
+#define DRV_VERSION		"1.6.0.56"
 #define PFX			DRV_NAME ": "
 #define DFX                     DRV_NAME "%d: "
 
···
 	unsigned int wq_count;
 	unsigned int cq_count;
 
+	struct mutex sgreset_mutex;
 	struct dentry *fnic_stats_debugfs_host;
 	struct dentry *fnic_stats_debugfs_file;
 	struct dentry *fnic_reset_debugfs_file;

drivers/scsi/fnic/fnic_scsi.c

···
 	struct reset_stats *reset_stats;
 	int tag = rq->tag;
 	DECLARE_COMPLETION_ONSTACK(tm_done);
-	int tag_gen_flag = 0;   /*to track tags allocated by fnic driver*/
 	bool new_sc = 0;
 
 	/* Wait for rport to unblock */
···
 	}
 
 	fnic_priv(sc)->flags = FNIC_DEVICE_RESET;
-	/* Allocate tag if not present */
 
 	if (unlikely(tag < 0)) {
 		/*
-		 * Really should fix the midlayer to pass in a proper
-		 * request for ioctls...
+		 * For device reset issued through sg3utils, we let
+		 * only one LUN_RESET to go through and use a special
+		 * tag equal to max_tag_id so that we don't have to allocate
+		 * or free it. It won't interact with tags
+		 * allocated by mid layer.
 		 */
-		tag = fnic_scsi_host_start_tag(fnic, sc);
-		if (unlikely(tag == SCSI_NO_TAG))
-			goto fnic_device_reset_end;
-		tag_gen_flag = 1;
+		mutex_lock(&fnic->sgreset_mutex);
+		tag = fnic->fnic_max_tag_id;
 		new_sc = 1;
 	}
 	io_lock = fnic_io_lock_hash(fnic, sc);
···
 		  (u64)sc->cmnd[4] << 8 | sc->cmnd[5]),
 		  fnic_flags_and_state(sc));
 
-	/* free tag if it is allocated */
-	if (unlikely(tag_gen_flag))
-		fnic_scsi_host_end_tag(fnic, sc);
+	if (new_sc)
+		mutex_unlock(&fnic->sgreset_mutex);
 
 	FNIC_SCSI_DBG(KERN_DEBUG, fnic->lport->host,
 		      "Returning from device reset %s\n",