[PATCH 6.1 272/609] ice: use READ_ONCE() to access cached PHC time

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sergey Temerkhanov <[email protected]>

commit 2915681b89f817677ab9f1166d95b595bc144f5f upstream.

ptp.cached_phc_time is a 64-bit value updated by a periodic work item
on one CPU and read locklessly on another.  On 32-bit or non-atomic
architectures this can result in a torn read.  Use READ_ONCE() to
enforce a single atomic load.

Fixes: 77a781155a65 ("ice: enable receive hardware timestamping")
Cc: [email protected]
Signed-off-by: Sergey Temerkhanov <[email protected]>
Signed-off-by: Aleksandr Loktionov <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Tested-by: Rinitha S <[email protected]> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/net/ethernet/intel/ice/ice_ptp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/ethernet/intel/ice/ice_ptp.c
+++ b/drivers/net/ethernet/intel/ice/ice_ptp.c
@@ -595,7 +595,7 @@ static u64 ice_ptp_extend_40b_ts(struct
 		return 0;
 	}
 
-	return ice_ptp_extend_32b_ts(pf->ptp.cached_phc_time,
+	return ice_ptp_extend_32b_ts(READ_ONCE(pf->ptp.cached_phc_time),
 				     (in_tstamp >> 8) & mask);
 }