linux-kernel - [PATCH 1/3] ath9k: Handle -ENOMEM on RX gracefully

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Date:	Tue, 2 Dec 2008 12:51:22 -0800
From:	"Luis R. Rodriguez" <lrodriguez@...eros.com>
To:	<stable@...nel.org>
CC:	<ath9k-devel@...ts.ath9k.org>, <linux-wireless@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <sfr@...b.auug.org.au>,
	"Luis R. Rodriguez" <lrodriguez@...eros.com>
Subject: [PATCH 1/3] ath9k: Handle -ENOMEM on RX gracefully

We would get an oops on RX on -ENOMEM by passing
NULL to the hardware on ath_rx_buf_link(). The oops
would look something like this:

ath_rx_tasklet
...
RIP: ath_rx_buf_link

We correct this by handling the allocation for the next
skb we will put in our RX tail directly on the ath_rx_tasklet()
*prior* to sending up the last hardware processed
skb. If we run out of memory this gauranteees we have
skbs to work with while it simply drops new received
frames.

Signed-off-by: Luis R. Rodriguez <lrodriguez@...eros.com>
---
 drivers/net/wireless/ath9k/recv.c |   18 ++++++++++++++----
 1 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/ath9k/recv.c b/drivers/net/wireless/ath9k/recv.c
index 0941589..a4f92b2 100644
--- a/drivers/net/wireless/ath9k/recv.c
+++ b/drivers/net/wireless/ath9k/recv.c
@@ -441,18 +441,16 @@ static void ath_rx_requeue(struct ath_softc *sc, struct sk_buff *skb)
  */
 static int ath_rx_indicate(struct ath_softc *sc,
 			   struct sk_buff *skb,
+			   struct sk_buff *nskb,
 			   struct ath_recv_status *status,
 			   u16 keyix)
 {
 	struct ath_buf *bf = ATH_RX_CONTEXT(skb)->ctx_rxbuf;
-	struct sk_buff *nskb;
 	int type;
 
 	/* indicate frame to the stack, which will free the old skb. */
 	type = ath__rx_indicate(sc, skb, status, keyix);
 
-	/* allocate a new skb and queue it to for H/W processing */
-	nskb = ath_rxbuf_alloc(sc, sc->sc_rxbufsize);
 	if (nskb != NULL) {
 		bf->bf_mpdu = nskb;
 		bf->bf_buf_addr = ath_skb_map_single(sc,
@@ -741,6 +739,7 @@ int ath_rx_tasklet(struct ath_softc *sc, int flush)
 	struct ath_desc *ds;
 	struct ieee80211_hdr *hdr;
 	struct sk_buff *skb = NULL;
+	struct sk_buff *nskb = NULL;
 	struct ath_recv_status rx_status;
 	struct ath_hal *ah = sc->sc_ah;
 	int type, rx_processed = 0;
@@ -963,6 +962,17 @@ int ath_rx_tasklet(struct ath_softc *sc, int flush)
 		 */
 		if (sc->sc_rxbufsize < ds->ds_rxstat.rs_datalen)
 			goto rx_next;
+
+		/* allocate a new skb and queue it to for H/W processing */
+		nskb = ath_rxbuf_alloc(sc, sc->sc_rxbufsize);
+
+		/* Diregard current RX'd frame and reuse the old skb */
+		if (!nskb) {
+			list_move_tail(&bf->list, &sc->sc_rxbuf);
+			ath_rx_buf_link(sc, bf);
+			goto rx_next;
+		}
+
 		/*
 		 * Sync and unmap the frame.  At this point we're
 		 * committed to passing the sk_buff somewhere so
@@ -1052,7 +1062,7 @@ int ath_rx_tasklet(struct ath_softc *sc, int flush)
 
 		/* Pass frames up to the stack. */
 
-		type = ath_rx_indicate(sc, skb,
+		type = ath_rx_indicate(sc, skb, nskb,
 			&rx_status, ds->ds_rxstat.rs_keyix);
 
 		/*
-- 
1.5.6.rc2.15.g457bb.dirty

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