On 5/26/2025 7:48 PM, Johan Hovold wrote:
Add the missing memory barriers to make sure that destination ring
descriptors are read after the head pointers to avoid using stale data
on weakly ordered architectures like aarch64.
Tested-on: WCN6855 hw2.1 WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.41
Fixes: d5c65159f289 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Cc: stable@xxxxxxxxxxxxxxx # 5.6
Signed-off-by: Johan Hovold <johan+linaro@xxxxxxxxxx>
---
drivers/net/wireless/ath/ath11k/dp_rx.c | 19 +++++++++++++++++++
drivers/net/wireless/ath/ath11k/dp_tx.c | 3 +++
2 files changed, 22 insertions(+)
diff --git a/drivers/net/wireless/ath/ath11k/dp_rx.c b/drivers/net/wireless/ath/ath11k/dp_rx.c
index ea2959305dec..dfe2d889c20f 100644
--- a/drivers/net/wireless/ath/ath11k/dp_rx.c
+++ b/drivers/net/wireless/ath/ath11k/dp_rx.c
@@ -3851,6 +3851,9 @@ int ath11k_dp_process_rx_err(struct ath11k_base *ab, struct napi_struct *napi,
ath11k_hal_srng_access_begin(ab, srng);
+ /* Make sure descriptor is read after the head pointer. */
+ dma_rmb();
+
Thanks Johan, for continuing to follow up on this issue. I have some
different opinions.
This change somewhat deviates from the fix approach described in
https://lore.kernel.org/all/20250321095219.19369-1-johan+linaro@xxxxxxxxxx/.
In this case, the descriptor might be accessed before it is updated or
while it is still being updated. Therefore, a dma_rmb() should be added
after the call to ath11k_hal_srng_dst_get_next_entry() and before
accessing ath11k_hal_ce_dst_status_get_length(), to ensure that the DMA
has completed before reading the descriptor.
However, in this patch, the memory barrier is used to protect the head
pointer (HP). I don't think a memory barrier is necessary for HP,
because even if an outdated HP is fetched,
ath11k_hal_srng_dst_get_next_entry() will return NULL and exit safely.
So, placing the memory barrier inside
ath11k_hal_srng_dst_get_next_entry() would be more appropriate.
@@ -678,6 +678,8 @@ u32 *ath11k_hal_srng_dst_get_next_entry(struct
ath11k_base *ab,
if (srng->flags & HAL_SRNG_FLAGS_CACHED)
ath11k_hal_srng_prefetch_desc(ab, srng);
+ dma_rmb();
+
return desc;
}
while (budget &&
(desc = ath11k_hal_srng_dst_get_next_entry(ab, srng))) {
struct hal_reo_dest_ring *reo_desc = (struct hal_reo_dest_ring *)desc;
@@ -4154,6 +4157,9 @@ int ath11k_dp_rx_process_wbm_err(struct ath11k_base *ab,
ath11k_hal_srng_access_begin(ab, srng);
+ /* Make sure descriptor is read after the head pointer. */
+ dma_rmb();
+
while (budget) {
rx_desc = ath11k_hal_srng_dst_get_next_entry(ab, srng);
if (!rx_desc)
@@ -4280,6 +4286,9 @@ int ath11k_dp_process_rxdma_err(struct ath11k_base *ab, int mac_id, int budget)
ath11k_hal_srng_access_begin(ab, srng);
+ /* Make sure descriptor is read after the head pointer. */
+ dma_rmb();
+
while (quota-- &&
(desc = ath11k_hal_srng_dst_get_next_entry(ab, srng))) {
ath11k_hal_rx_reo_ent_paddr_get(ab, desc, &paddr, &desc_bank);
@@ -4353,6 +4362,9 @@ void ath11k_dp_process_reo_status(struct ath11k_base *ab)
ath11k_hal_srng_access_begin(ab, srng);
+ /* Make sure descriptor is read after the head pointer. */
+ dma_rmb();
+
while ((reo_desc = ath11k_hal_srng_dst_get_next_entry(ab, srng))) {
tag = FIELD_GET(HAL_SRNG_TLV_HDR_TAG, *reo_desc);
@@ -5168,6 +5180,9 @@ static void ath11k_dp_rx_mon_dest_process(struct ath11k *ar, int mac_id,
rx_bufs_used = 0;
rx_mon_stats = &pmon->rx_mon_stats;
+ /* Make sure descriptor is read after the head pointer. */
+ dma_rmb();
+
while ((ring_entry = ath11k_hal_srng_dst_peek(ar->ab, mon_dst_srng))) {
struct sk_buff *head_msdu, *tail_msdu;
@@ -5630,6 +5645,10 @@ static int ath11k_dp_full_mon_process_rx(struct ath11k_base *ab, int mac_id,
spin_lock_bh(&mon_dst_srng->lock);
ath11k_hal_srng_access_begin(ar->ab, mon_dst_srng);
+
+ /* Make sure descriptor is read after the head pointer. */
+ dma_rmb();
+
while ((ring_entry = ath11k_hal_srng_dst_peek(ar->ab, mon_dst_srng))) {
head_msdu = NULL;
tail_msdu = NULL;
diff --git a/drivers/net/wireless/ath/ath11k/dp_tx.c b/drivers/net/wireless/ath/ath11k/dp_tx.c
index 8522c67baabf..549d17d90503 100644
--- a/drivers/net/wireless/ath/ath11k/dp_tx.c
+++ b/drivers/net/wireless/ath/ath11k/dp_tx.c
@@ -700,6 +700,9 @@ void ath11k_dp_tx_completion_handler(struct ath11k_base *ab, int ring_id)
ath11k_hal_srng_access_begin(ab, status_ring);
+ /* Make sure descriptor is read after the head pointer. */
+ dma_rmb();
+
while ((ATH11K_TX_COMPL_NEXT(tx_ring->tx_status_head) !=
tx_ring->tx_status_tail) &&
(desc = ath11k_hal_srng_dst_get_next_entry(ab, status_ring))) {
