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From:   Ramya Gnanasekar <quic_rgnanase@quicinc.com>
To:     ath12k@lists.infradead.org
Cc:     linux-wireless@vger.kernel.org, Karthik M <quic_karm@quicinc.com>,
        Ramya Gnanasekar <quic_rgnanase@quicinc.com>
Subject: [PATCH] wifi: ath12k: fix potential wmi_mgmt_tx_queue race condition
Date:   Mon,  3 Apr 2023 22:48:06 +0530
Message-Id: <20230403171806.12805-1-quic_rgnanase@quicinc.com>
Precedence: bulk

From: Karthik M <quic_karm@quicinc.com>

During stress test with maximum VAPs and peer connected, below warning
is seen:

[ 1079.110967] ath12k_pci 0004:01:00.0: mgmt tx queue is full
[ 1079.117708] ath12k_pci 0004:01:00.0: failed to queue management frame -28
[ 1079.123191] ath12k_pci 0004:01:00.0: mgmt tx queue is full
[ 1079.129960] ath12k_pci 0004:01:00.0: failed to queue management frame -28
[ 1079.135641] ath12k_pci 0004:01:00.0: mgmt tx queue is full

This is caused by potential race condition while accessing skb_queue_len().
When ath12k_mgmt_over_wmi_tx_work() and ath12k_mac_mgmt_tx() is called concurrently,
then skb_queue_len() might fetch list length which is modified by skb_queue_tail()
or skb_dequeue().

Replace skb_queue_len() with skb_queue_len_lockless() which will
prevent concurrent modified access using READ_ONCE(). And also use '>=',
in case we queue a few SKBs simultaneously.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1

Signed-off-by: Karthik M <quic_karm@quicinc.com>
Signed-off-by: Ramya Gnanasekar <quic_rgnanase@quicinc.com>

diff --git a/drivers/net/wireless/ath/ath12k/mac.c b/drivers/net/wireless/ath/ath12k/mac.c
index 0e5cc477ba56..cc458fed5e78 100644
--- a/drivers/net/wireless/ath/ath12k/mac.c
+++ b/drivers/net/wireless/ath/ath12k/mac.c
@@ -4489,7 +4489,7 @@ static int ath12k_mac_mgmt_tx(struct ath12k *ar, struct sk_buff *skb,
 		return -ENOSPC;
 	}
 
-	if (skb_queue_len(q) == ATH12K_TX_MGMT_NUM_PENDING_MAX) {
+	if (skb_queue_len_lockless(q) >= ATH12K_TX_MGMT_NUM_PENDING_MAX) {
 		ath12k_warn(ar->ab, "mgmt tx queue is full\n");
 		return -ENOSPC;
 	}
-- 
2.17.1