ath11k: Fixing dangling pointer issue upon peer delete failure

When there is WMI command failure, 'peer->sta' was not getting
cleaned up, and mac80211 frees the 'sta' memory, which is causing
the below page fault.

Cleaning up the sta pointer in ath11k whenever peer delete command
is sent.

Unable to handle kernel paging request at virtual address 200080000006a
pgd = ffffffc02a774000
[200080000006a] *pgd=0000000000000000, *pud=0000000000000000
Internal error: Oops: 96000004 [#1] PREEMPT SMP
.
.
.
CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W       4.4.60 #1
Hardware name: Qualcomm Technologies, Inc. IPQ807x/AP-HK01-C1 (DT)
task: ffffffc00083c6d0 ti: ffffffc00083c6d0 task.ti: ffffffc00083c6d0
PC is at ath11k_dp_rx_process_mon_status+0x114/0x4e0 [ath11k]
LR is at ath11k_dp_rx_process_mon_status+0xe8/0x4e0 [ath11k]
pc : [<ffffffbffcf8e544>] lr : [<ffffffbffcf8e518>] pstate: 60000145
sp : ffffffc000833a30
Signed-off-by: Vikas Patel <vikpatel@codeaurora.org>
Signed-off-by: Venkateswara Naralasetty <vnaralas@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/ath11k/mac.c

@@ -2786,6 +2786,7 @@ static int ath11k_mac_op_sta_state(struct ieee80211_hw *hw,
 	struct ath11k *ar = hw->priv;
 	struct ath11k_vif *arvif = ath11k_vif_to_arvif(vif);
 	struct ath11k_sta *arsta = (struct ath11k_sta *)sta->drv_priv;
+	struct ath11k_peer *peer;
 	int ret = 0;
 
 	/* cancel must be done outside the mutex to avoid deadlock */
@@ -2818,6 +2819,17 @@ static int ath11k_mac_op_sta_state(struct ieee80211_hw *hw,
 				   sta->addr, arvif->vdev_id);
 
 		ath11k_mac_dec_num_stations(arvif, sta);
+		spin_lock_bh(&ar->ab->base_lock);
+		peer = ath11k_peer_find(ar->ab, arvif->vdev_id, sta->addr);
+		if (peer && peer->sta == sta) {
+			ath11k_warn(ar->ab, "Found peer entry %pM n vdev %i after it was supposedly removed\n",
+				    vif->addr, arvif->vdev_id);
+			peer->sta = NULL;
+			list_del(&peer->list);
+			kfree(peer);
+			ar->num_peers--;
+		}
+		spin_unlock_bh(&ar->ab->base_lock);
 
 		kfree(arsta->tx_stats);
 		arsta->tx_stats = NULL;