scsi: pm80xx: Set phy->enable_completion only when we wait for it

pm8001_phy_control() populates the enable_completion pointer with a stack
address, sends a PHY_LINK_RESET / PHY_HARD_RESET, waits 300 ms, and
returns. The problem arises when a phy control response comes late.  After
300 ms the pm8001_phy_control() function returns and the passed
enable_completion stack address is no longer valid. Late phy control
response invokes complete() on a dangling enable_completion pointer which
leads to a kernel crash.
Signed-off-by: Igor Pylypiv <ipylypiv@google.com>
Signed-off-by: Terrence Adams <tadamsjr@google.com>
Link: https://lore.kernel.org/r/20240627155924.2361370-2-tadamsjr@google.comAcked-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/pm8001/pm8001_sas.c

@@ -166,7 +166,6 @@ int pm8001_phy_control(struct asd_sas_phy *sas_phy, enum phy_func func,
 	unsigned long flags;
 	pm8001_ha = sas_phy->ha->lldd_ha;
 	phy = &pm8001_ha->phy[phy_id];
-	pm8001_ha->phy[phy_id].enable_completion = &completion;
 
 	if (PM8001_CHIP_DISP->fatal_errors(pm8001_ha)) {
 		/*
@@ -190,6 +189,7 @@ int pm8001_phy_control(struct asd_sas_phy *sas_phy, enum phy_func func,
 				rates->maximum_linkrate;
 		}
 		if (pm8001_ha->phy[phy_id].phy_state ==  PHY_LINK_DISABLE) {
+			pm8001_ha->phy[phy_id].enable_completion = &completion;
 			PM8001_CHIP_DISP->phy_start_req(pm8001_ha, phy_id);
 			wait_for_completion(&completion);
 		}
@@ -198,6 +198,7 @@ int pm8001_phy_control(struct asd_sas_phy *sas_phy, enum phy_func func,
 		break;
 	case PHY_FUNC_HARD_RESET:
 		if (pm8001_ha->phy[phy_id].phy_state == PHY_LINK_DISABLE) {
+			pm8001_ha->phy[phy_id].enable_completion = &completion;
 			PM8001_CHIP_DISP->phy_start_req(pm8001_ha, phy_id);
 			wait_for_completion(&completion);
 		}
@@ -206,6 +207,7 @@ int pm8001_phy_control(struct asd_sas_phy *sas_phy, enum phy_func func,
 		break;
 	case PHY_FUNC_LINK_RESET:
 		if (pm8001_ha->phy[phy_id].phy_state == PHY_LINK_DISABLE) {
+			pm8001_ha->phy[phy_id].enable_completion = &completion;
 			PM8001_CHIP_DISP->phy_start_req(pm8001_ha, phy_id);
 			wait_for_completion(&completion);
 		}