ath9k: fix invalid descriptor discarding

Only set sc->rx.discard_next to rx_stats->rs_more when actually
discarding the current descriptor.

Also, fix a detection of broken descriptors:
First the code checks if the current descriptor is not done.
Then it checks if the next descriptor is done.
Add a check that afterwards checks the first descriptor again, because
it might have been completed in the mean time.

This fixes a regression introduced in
commit 723e7113
"ath9k: fix handling of broken descriptors"

Cc: stable@vger.kernel.org
Reported-by: Marco André Dinis <marcoandredinis@gmail.com>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/recv.c

@@ -731,6 +731,12 @@ static struct ath_rxbuf *ath_get_next_rx_buf(struct ath_softc *sc,
 		if (ret == -EINPROGRESS)
 			return NULL;
 
+		/*
+		 * Re-check previous descriptor, in case it has been filled
+		 * in the mean time.
+		 */
+		ret = ath9k_hw_rxprocdesc(ah, ds, rs);
+		if (ret == -EINPROGRESS) {
 			/*
 			 * mark descriptor as zero-length and set the 'more'
 			 * flag to ensure that both buffers get discarded
@@ -738,6 +744,7 @@ static struct ath_rxbuf *ath_get_next_rx_buf(struct ath_softc *sc,
 			rs->rs_datalen = 0;
 			rs->rs_more = true;
 		}
+	}
 
 	list_del(&bf->list);
 	if (!bf->bf_mpdu)
@@ -985,22 +992,22 @@ static int ath9k_rx_skb_preprocess(struct ath_softc *sc,
 	struct ath_common *common = ath9k_hw_common(ah);
 	struct ieee80211_hdr *hdr;
 	bool discard_current = sc->rx.discard_next;
-	int ret = 0;
 
 	/*
 	 * Discard corrupt descriptors which are marked in
 	 * ath_get_next_rx_buf().
 	 */
-	sc->rx.discard_next = rx_stats->rs_more;
 	if (discard_current)
-		return -EINVAL;
+		goto corrupt;
+
+	sc->rx.discard_next = false;
 
 	/*
 	 * Discard zero-length packets.
 	 */
 	if (!rx_stats->rs_datalen) {
 		RX_STAT_INC(rx_len_err);
-		return -EINVAL;
+		goto corrupt;
 	}
 
 	/*
@@ -1010,7 +1017,7 @@ static int ath9k_rx_skb_preprocess(struct ath_softc *sc,
 	 */
 	if (rx_stats->rs_datalen > (common->rx_bufsize - ah->caps.rx_status_len)) {
 		RX_STAT_INC(rx_len_err);
-		return -EINVAL;
+		goto corrupt;
 	}
 
 	/* Only use status info from the last fragment */
@@ -1024,10 +1031,8 @@ static int ath9k_rx_skb_preprocess(struct ath_softc *sc,
 	 * This is different from the other corrupt descriptor
 	 * condition handled above.
 	 */
-	if (rx_stats->rs_status & ATH9K_RXERR_CORRUPT_DESC) {
-		ret = -EINVAL;
-		goto exit;
-	}
+	if (rx_stats->rs_status & ATH9K_RXERR_CORRUPT_DESC)
+		goto corrupt;
 
 	hdr = (struct ieee80211_hdr *) (skb->data + ah->caps.rx_status_len);
 
@@ -1043,18 +1048,15 @@ static int ath9k_rx_skb_preprocess(struct ath_softc *sc,
 		if (ath_process_fft(sc, hdr, rx_stats, rx_status->mactime))
 			RX_STAT_INC(rx_spectral);
 
-		ret = -EINVAL;
-		goto exit;
+		return -EINVAL;
 	}
 
 	/*
 	 * everything but the rate is checked here, the rate check is done
 	 * separately to avoid doing two lookups for a rate for each frame.
 	 */
-	if (!ath9k_rx_accept(common, hdr, rx_status, rx_stats, decrypt_error)) {
-		ret = -EINVAL;
-		goto exit;
-	}
+	if (!ath9k_rx_accept(common, hdr, rx_status, rx_stats, decrypt_error))
+		return -EINVAL;
 
 	if (ath_is_mybeacon(common, hdr)) {
 		RX_STAT_INC(rx_beacons);
@@ -1064,15 +1066,11 @@ static int ath9k_rx_skb_preprocess(struct ath_softc *sc,
 	/*
 	 * This shouldn't happen, but have a safety check anyway.
 	 */
-	if (WARN_ON(!ah->curchan)) {
-		ret = -EINVAL;
-		goto exit;
-	}
+	if (WARN_ON(!ah->curchan))
+		return -EINVAL;
 
-	if (ath9k_process_rate(common, hw, rx_stats, rx_status)) {
-		ret =-EINVAL;
-		goto exit;
-	}
+	if (ath9k_process_rate(common, hw, rx_stats, rx_status))
+		return -EINVAL;
 
 	ath9k_process_rssi(common, hw, rx_stats, rx_status);
 
@@ -1087,9 +1085,11 @@ static int ath9k_rx_skb_preprocess(struct ath_softc *sc,
 		sc->rx.num_pkts++;
 #endif
 
-exit:
-	sc->rx.discard_next = false;
-	return ret;
+	return 0;
+
+corrupt:
+	sc->rx.discard_next = rx_stats->rs_more;
+	return -EINVAL;
 }
 
 static void ath9k_rx_skb_postprocess(struct ath_common *common,