ice: Fix PTP NULL pointer dereference during VSI rebuild

Fix race condition where PTP periodic work runs while VSI is being
rebuilt, accessing NULL vsi->rx_rings.

The sequence was:
1. ice_ptp_prepare_for_reset() cancels PTP work
2. ice_ptp_rebuild() immediately queues PTP work
3. VSI rebuild happens AFTER ice_ptp_rebuild()
4. PTP work runs and accesses NULL vsi->rx_rings

Fix: Keep PTP work cancelled during rebuild, only queue it after
VSI rebuild completes in ice_rebuild().

Added ice_ptp_queue_work() helper function to encapsulate the logic
for queuing PTP work, ensuring it's only queued when PTP is supported
and the state is ICE_PTP_READY.

Error log:
[ 121.392544] ice 0000:60:00.1: PTP reset successful
[ 121.392692] BUG: kernel NULL pointer dereference, address: 0000000000000000
[ 121.392712] #PF: supervisor read access in kernel mode
[ 121.392720] #PF: error_code(0x0000) - not-present page
[ 121.392727] PGD 0
[ 121.392734] Oops: Oops: 0000 [#1] SMP NOPTI
[ 121.392746] CPU: 8 UID: 0 PID: 1005 Comm: ice-ptp-0000:60 Tainted: G S 6.19.0-rc6+ #4 PREEMPT(voluntary)
[ 121.392761] Tainted: [S]=CPU_OUT_OF_SPEC
[ 121.392773] RIP: 0010:ice_ptp_update_cached_phctime+0xbf/0x150 [ice]
[ 121.393042] Call Trace:
[ 121.393047] <TASK>
[ 121.393055] ice_ptp_periodic_work+0x69/0x180 [ice]
[ 121.393202] kthread_worker_fn+0xa2/0x260
[ 121.393216] ? __pfx_ice_ptp_periodic_work+0x10/0x10 [ice]
[ 121.393359] ? __pfx_kthread_worker_fn+0x10/0x10
[ 121.393371] kthread+0x10d/0x230
[ 121.393382] ? __pfx_kthread+0x10/0x10
[ 121.393393] ret_from_fork+0x273/0x2b0
[ 121.393407] ? __pfx_kthread+0x10/0x10
[ 121.393417] ret_from_fork_asm+0x1a/0x30
[ 121.393432] </TASK>

Fixes: 803bef817807d ("ice: factor out ice_ptp_rebuild_owner()")
Signed-off-by: Aaron Ma <[e-mail]>
Tested-by: Sunitha Mekala <[e-mail]> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <[e-mail]>

drivers/net/ethernet/intel/ice/ice_main.c

···
 
 	/* Restore timestamp mode settings after VSI rebuild */
 	ice_ptp_restore_timestamp_mode(pf);
+
+	/* Start PTP periodic work after VSI is fully rebuilt */
+	ice_ptp_queue_work(pf);
 	return;
 
 err_vsi_rebuild:

drivers/net/ethernet/intel/ice/ice_ptp.c

···
 }
 
 /**
+ * ice_ptp_queue_work - Queue PTP periodic work for a PF
+ * @pf: Board private structure
+ *
+ * Helper function to queue PTP periodic work after VSI rebuild completes.
+ * This ensures that PTP work only runs when VSI structures are ready.
+ */
+void ice_ptp_queue_work(struct ice_pf *pf)
+{
+	if (test_bit(ICE_FLAG_PTP_SUPPORTED, pf->flags) &&
+	    pf->ptp.state == ICE_PTP_READY)
+		kthread_queue_delayed_work(pf->ptp.kworker, &pf->ptp.work, 0);
+}
+
+/**
  * ice_ptp_prepare_rebuild_sec - Prepare second NAC for PTP reset or rebuild
  * @pf: Board private structure
  * @rebuild: rebuild if true, prepare if false
···
 		struct ice_pf *peer_pf = ptp_port_to_pf(port);
 
 		if (!ice_is_primary(&peer_pf->hw)) {
-			if (rebuild)
+			if (rebuild) {
+				/* TODO: When implementing rebuild=true:
+				 * 1. Ensure secondary PFs' VSIs are rebuilt
+				 * 2. Call ice_ptp_queue_work(peer_pf) after VSI rebuild
+				 */
 				ice_ptp_rebuild(peer_pf, reset_type);
-			else
+			} else {
 				ice_ptp_prepare_for_reset(peer_pf, reset_type);
+			}
 		}
 	}
 }
···
 	}
 
 	ptp->state = ICE_PTP_READY;
-
-	/* Start periodic work going */
-	kthread_queue_delayed_work(ptp->kworker, &ptp->work, 0);
 
 	dev_info(ice_pf_to_dev(pf), "PTP reset successful\n");
 	return;

drivers/net/ethernet/intel/ice/ice_ptp.h

···
 void ice_ptp_init(struct ice_pf *pf);
 void ice_ptp_release(struct ice_pf *pf);
 void ice_ptp_link_change(struct ice_pf *pf, bool linkup);
+void ice_ptp_queue_work(struct ice_pf *pf);
 #else /* IS_ENABLED(CONFIG_PTP_1588_CLOCK) */
 
 static inline int ice_ptp_hwtstamp_get(struct net_device *netdev,
···
 static inline void ice_ptp_init(struct ice_pf *pf) { }
 static inline void ice_ptp_release(struct ice_pf *pf) { }
 static inline void ice_ptp_link_change(struct ice_pf *pf, bool linkup)
+{
+}
+
+static inline void ice_ptp_queue_work(struct ice_pf *pf)
 {
 }