[PATCH ath-next 4/6] wifi: ath12k: place dp_mon_mpdu on stack in mon dst reap loop

[Kang Yang]

ath12k_wifi7_dp_rx_mon_dest_process() allocates a dp_mon_mpdu with
kzalloc(GFP_ATOMIC) for each delivered MPDU. On allocation failure
it breaks out of the reap loop without calling
ath12k_hal_srng_dst_get_next_entry(), leaving the destination ring
tail pointer parked on the current entry -- the same entry will
be peek()ed on every subsequent NAPI schedule, stalling monitor
RX until the mon_dest_ring_stuck_cnt recovery path resyncs the
PPDU ID. The head_msdu chain accumulated for this iteration is
also orphaned since the break bypasses both the delivery and
the cleanup paths.

kmemleak reports these skbs in field testing:
  kmemleak_alloc()
  __netdev_alloc_skb()
  ath12k_dp_rx_bufs_replenish()
  ath12k_wifi7_dp_rx_mon_dest_process()

dp_mon_mpdu is used only within a single reap loop iteration and
is passed synchronously to ath12k_wifi7_dp_mon_rx_deliver(); the
callee does not retain the pointer. Place it on the stack instead
of using kzalloc(GFP_ATOMIC). This eliminates the allocation
failure path (and the ring stall it caused) and saves a
kzalloc/kfree pair per delivered MPDU.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.1.c7-00108-QCAHMTSWPL_V1.0_V2.0_SILICONZ_UPSTREAM-3

Fixes: 72bfbf19b7da ("wifi: ath12k: add support to reap and process mon dest ring")
Signed-off-by: Kang Yang <kang.yang at oss.qualcomm.com>
---
 .../net/wireless/ath/ath12k/wifi7/dp_mon.c    | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/net/wireless/ath/ath12k/wifi7/dp_mon.c b/drivers/net/wireless/ath/ath12k/wifi7/dp_mon.c
index 8fca777041d1..1e29c13ad66d 100644
--- a/drivers/net/wireless/ath/ath12k/wifi7/dp_mon.c
+++ b/drivers/net/wireless/ath/ath12k/wifi7/dp_mon.c
@@ -2827,7 +2827,6 @@ ath12k_wifi7_dp_rx_mon_dest_process(struct ath12k *ar, int mac_id,
 	struct ath12k_base *ab = ar->ab;
 	struct ath12k_dp *dp = ath12k_ab_to_dp(ab);
 	void *ring_entry, *mon_dst_srng;
-	struct dp_mon_mpdu *tmp_mpdu;
 	LIST_HEAD(rx_desc_used_list);
 	struct hal_srng *srng;
 
@@ -2893,18 +2892,16 @@ ath12k_wifi7_dp_rx_mon_dest_process(struct ath12k *ar, int mac_id,
 		}
 
 		if (head_msdu && tail_msdu) {
-			tmp_mpdu = kzalloc_obj(*tmp_mpdu, GFP_ATOMIC);
-			if (!tmp_mpdu)
-				break;
-
-			tmp_mpdu->head = head_msdu;
-			tmp_mpdu->tail = tail_msdu;
-			tmp_mpdu->err_bitmap = pmon->err_bitmap;
-			tmp_mpdu->decap_format = pmon->decap_format;
-			ath12k_wifi7_dp_mon_rx_deliver(&ar->dp, tmp_mpdu,
+			struct dp_mon_mpdu tmp_mpdu = {
+				.head = head_msdu,
+				.tail = tail_msdu,
+				.err_bitmap = pmon->err_bitmap,
+				.decap_format = pmon->decap_format,
+			};
+
+			ath12k_wifi7_dp_mon_rx_deliver(&ar->dp, &tmp_mpdu,
 						       &pmon->mon_ppdu_info, napi);
 			rx_mon_stats->dest_mpdu_done++;
-			kfree(tmp_mpdu);
 		}
 
 		ring_entry = ath12k_hal_srng_dst_get_next_entry(ar->ab,
-- 
2.34.1