[ 3.8.y.z extended stable ] Patch "ath9k: fix rx descriptor related race condition" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ath9k: fix rx descriptor related race condition

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.10.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From e2306b816ba1f968b0dc3c45b2ea84609b3e1e18 Mon Sep 17 00:00:00 2001
From: Felix Fietkau <nbd at openwrt.org>
Date: Sat, 10 Aug 2013 15:59:15 +0200
Subject: ath9k: fix rx descriptor related race condition

commit e96542e55a2aacf4bdeccfe2f17b77c4895b4df2 upstream.

Similar to a race condition that exists in the tx path, the hardware
might re-read the 'next' pointer of a descriptor of the last completed
frame. This only affects non-EDMA (pre-AR93xx) devices.

To deal with this race, defer clearing and re-linking a completed rx
descriptor until the next one has been processed.

Signed-off-by: Felix Fietkau <nbd at openwrt.org>
Signed-off-by: John W. Linville <linville at tuxdriver.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/net/wireless/ath/ath9k/ath9k.h |  5 +----
 drivers/net/wireless/ath/ath9k/recv.c  | 17 +++++++++++++----
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/drivers/net/wireless/ath/ath9k/ath9k.h b/drivers/net/wireless/ath/ath9k/ath9k.h
index 42794c5..46e1fa7 100644
--- a/drivers/net/wireless/ath/ath9k/ath9k.h
+++ b/drivers/net/wireless/ath/ath9k/ath9k.h
@@ -79,10 +79,6 @@ struct ath_config {
 		       sizeof(struct ath_buf_state));		\
 	} while (0)

-#define ATH_RXBUF_RESET(_bf) do {		\
-		(_bf)->bf_stale = false;	\
-	} while (0)
-
 /**
  * enum buffer_type - Buffer type flags
  *
@@ -322,6 +318,7 @@ struct ath_rx {
 	struct ath_buf *rx_bufptr;
 	struct ath_rx_edma rx_edma[ATH9K_RX_QUEUE_MAX];

+	struct ath_buf *buf_hold;
 	struct sk_buff *frag;
 };

diff --git a/drivers/net/wireless/ath/ath9k/recv.c b/drivers/net/wireless/ath/ath9k/recv.c
index 90752f2..262491d 100644
--- a/drivers/net/wireless/ath/ath9k/recv.c
+++ b/drivers/net/wireless/ath/ath9k/recv.c
@@ -41,8 +41,6 @@ static void ath_rx_buf_link(struct ath_softc *sc, struct ath_buf *bf)
 	struct ath_desc *ds;
 	struct sk_buff *skb;

-	ATH_RXBUF_RESET(bf);
-
 	ds = bf->bf_desc;
 	ds->ds_link = 0; /* link to null */
 	ds->ds_data = bf->bf_buf_addr;
@@ -69,6 +67,14 @@ static void ath_rx_buf_link(struct ath_softc *sc, struct ath_buf *bf)
 	sc->rx.rxlink = &ds->ds_link;
 }

+static void ath_rx_buf_relink(struct ath_softc *sc, struct ath_buf *bf)
+{
+	if (sc->rx.buf_hold)
+		ath_rx_buf_link(sc, sc->rx.buf_hold);
+
+	sc->rx.buf_hold = bf;
+}
+
 static void ath_setdefantenna(struct ath_softc *sc, u32 antenna)
 {
 	/* XXX block beacon interrupts */
@@ -116,7 +122,6 @@ static bool ath_rx_edma_buf_link(struct ath_softc *sc,

 	skb = bf->bf_mpdu;

-	ATH_RXBUF_RESET(bf);
 	memset(skb->data, 0, ah->caps.rx_status_len);
 	dma_sync_single_for_device(sc->dev, bf->bf_buf_addr,
 				ah->caps.rx_status_len, DMA_TO_DEVICE);
@@ -444,6 +449,7 @@ int ath_startrecv(struct ath_softc *sc)
 	if (list_empty(&sc->rx.rxbuf))
 		goto start_recv;

+	sc->rx.buf_hold = NULL;
 	sc->rx.rxlink = NULL;
 	list_for_each_entry_safe(bf, tbf, &sc->rx.rxbuf, list) {
 		ath_rx_buf_link(sc, bf);
@@ -689,6 +695,9 @@ static struct ath_buf *ath_get_next_rx_buf(struct ath_softc *sc,
 	}

 	bf = list_first_entry(&sc->rx.rxbuf, struct ath_buf, list);
+	if (bf == sc->rx.buf_hold)
+		return NULL;
+
 	ds = bf->bf_desc;

 	/*
@@ -1238,7 +1247,7 @@ requeue:
 		if (edma) {
 			ath_rx_edma_buf_link(sc, qtype);
 		} else {
-			ath_rx_buf_link(sc, bf);
+			ath_rx_buf_relink(sc, bf);
 			ath9k_hw_rxena(ah);
 		}
 	} while (1);
--
1.8.1.2