scsi: lpfc: Prevent NDLP reference count underflow in dev_loss_tmo callback

Current dev_loss_tmo handling checks whether there has been a previous
call to unregister with SCSI transport.  If so, the NDLP kref count is
decremented a second time in dev_loss_tmo as the final kref release.
However, this can sometimes result in a reference count underflow if
there is also a race to unregister with NVMe transport as well.  Add a
check for NVMe transport registration before decrementing the final
kref.  If NVMe transport is still registered, then the NVMe transport
unregistration is designated as the final kref decrement.

Signed-off-by: Justin Tee <justin.tee@broadcom.com>
Link: https://lore.kernel.org/r/20241031223219.152342-8-justintee8345@gmail.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Justin Tee

drivers/scsi/lpfc/lpfc_hbadisc.c

@@ -161,6 +161,7 @@ lpfc_dev_loss_tmo_callbk(struct fc_rport *rport)
 	struct lpfc_hba   *phba;
 	struct lpfc_work_evt *evtp;
 	unsigned long iflags;
+	bool nvme_reg = false;
 
 	ndlp = ((struct lpfc_rport_data *)rport->dd_data)->pnode;
 	if (!ndlp)
@@ -183,38 +184,49 @@ lpfc_dev_loss_tmo_callbk(struct fc_rport *rport)
 	/* Don't schedule a worker thread event if the vport is going down. */
 	if (test_bit(FC_UNLOADING, &vport->load_flag) ||
 	    !test_bit(HBA_SETUP, &phba->hba_flag)) {
+
 		spin_lock_irqsave(&ndlp->lock, iflags);
 		ndlp->rport = NULL;
 
+		if (ndlp->fc4_xpt_flags & NVME_XPT_REGD)
+			nvme_reg = true;
+
 		/* The scsi_transport is done with the rport so lpfc cannot
-		 * call to unregister. Remove the scsi transport reference
-		 * and clean up the SCSI transport node details.
+		 * call to unregister.
 		 */
-		if (ndlp->fc4_xpt_flags & (NLP_XPT_REGD | SCSI_XPT_REGD)) {
+		if (ndlp->fc4_xpt_flags & SCSI_XPT_REGD) {
 			ndlp->fc4_xpt_flags &= ~SCSI_XPT_REGD;
 
-			/* NVME transport-registered rports need the
-			 * NLP_XPT_REGD flag to complete an unregister.
+			/* If NLP_XPT_REGD was cleared in lpfc_nlp_unreg_node,
+			 * unregister calls were made to the scsi and nvme
+			 * transports and refcnt was already decremented. Clear
+			 * the NLP_XPT_REGD flag only if the NVME Rport is
+			 * confirmed unregistered.
 			 */
-			if (!(ndlp->fc4_xpt_flags & NVME_XPT_REGD))
+			if (!nvme_reg && ndlp->fc4_xpt_flags & NLP_XPT_REGD) {
 				ndlp->fc4_xpt_flags &= ~NLP_XPT_REGD;
+				spin_unlock_irqrestore(&ndlp->lock, iflags);
+				lpfc_nlp_put(ndlp); /* may free ndlp */
+			} else {
+				spin_unlock_irqrestore(&ndlp->lock, iflags);
+			}
+		} else {
 			spin_unlock_irqrestore(&ndlp->lock, iflags);
-			lpfc_nlp_put(ndlp);
-			spin_lock_irqsave(&ndlp->lock, iflags);
 		}
 
+		spin_lock_irqsave(&ndlp->lock, iflags);
+
 		/* Only 1 thread can drop the initial node reference.  If
 		 * another thread has set NLP_DROPPED, this thread is done.
 		 */
-		if (!(ndlp->fc4_xpt_flags & NVME_XPT_REGD) &&
-		    !(ndlp->nlp_flag & NLP_DROPPED)) {
-			ndlp->nlp_flag |= NLP_DROPPED;
+		if (nvme_reg || (ndlp->nlp_flag & NLP_DROPPED)) {
 			spin_unlock_irqrestore(&ndlp->lock, iflags);
-			lpfc_nlp_put(ndlp);
 			return;
 		}
 
+		ndlp->nlp_flag |= NLP_DROPPED;
 		spin_unlock_irqrestore(&ndlp->lock, iflags);
+		lpfc_nlp_put(ndlp);
 		return;
 	}