On Sat, 10 Jan 2009, Bob Copeland wrote:
> On Sat, Jan 10, 2009 at 11:47:05AM -0500, Bob Copeland wrote:
> > Well I got a lockup doing that, I'll try again later but anyway I see
> > the bug already, read on if interested. I should have a patch shortly.
>
> Err, of course I would get a lockup, it's a BUG_ON. This patch seems to
> fix it for me.
>
> From: Bob Copeland <me@xxxxxxxxxxxxxxx>
> Date: Sat, 10 Jan 2009 14:42:54 -0500
> Subject: [PATCH] ath5k: fix bf->skb==NULL panic in ath5k_tasklet_rx
>
> Under memory pressure, we may not be able to allocate a new skb for
> new packets. If the allocation fails, ath5k_tasklet_rx will exit but
> will leave a buffer in the list with a NULL skb, eventually triggering
> a BUG_ON.
>
> Extract the skb allocation from ath5k_rxbuf_setup() and change the
> tasklet to allocate the next skb before accepting a packet.
Thanks a lot, Bob, this looks like it should work.
But I haven't seen any allocation failure for several days.
I didn't get any while trying to simplify the reproduction,
and so once your patch arrived I switched back to trying my
original load with your patch applied.
That's so far had three runs (one on 2.6.28, two on 2.6.29-rc1) of
about 16 hours each, without even hitting the origin of the problem.
I did say originally that it would take a week or two to confirm,
so I'll just keep on trying.
I guess we can see from the nature of your patch that it has to
fix it; but it still would be nice to see such an allocation
failure logged, and the system and its wireless continuing okay.
>
> Changes-licensed-under: 3-Clause-BSD
Hmm, I haven't noticed anyone doing that before: hope you're not
starting a trend! I think you'll find (Documentation/SubmittingPatches)
that your Signed-off-by agrees to the Developer's Certificate of Origin
1.1, which would put your patch under the same open source licence(s) as
drivers/net/wireless/ath5k/base.c already contains - that's the usual
case.
But IANAL, and I may be missing an important nuance you'd hoped to convey:
that "(unless I am permitted to submit under a different licence)" clause?
Hugh
>
> Signed-off-by: Bob Copeland <me@xxxxxxxxxxxxxxx>
> ---
> drivers/net/wireless/ath5k/base.c | 85 +++++++++++++++++++++++--------------
> 1 files changed, 53 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/net/wireless/ath5k/base.c b/drivers/net/wireless/ath5k/base.c
> index 2b7b7f6..1c0061a 100644
> --- a/drivers/net/wireless/ath5k/base.c
> +++ b/drivers/net/wireless/ath5k/base.c
> @@ -1095,6 +1095,42 @@ ath5k_hw_to_driver_rix(struct ath5k_softc *sc, int hw_rix)
> * Buffers setup *
> \***************/
>
> +static
> +struct sk_buff *ath5k_rx_skb_alloc(struct ath5k_softc *sc, dma_addr_t *skb_addr)
> +{
> + struct sk_buff *skb;
> + unsigned int off;
> +
> + /*
> + * Allocate buffer with headroom_needed space for the
> + * fake physical layer header at the start.
> + */
> + skb = dev_alloc_skb(sc->rxbufsize + sc->cachelsz - 1);
> +
> + if (!skb) {
> + ATH5K_ERR(sc, "can't alloc skbuff of size %u\n",
> + sc->rxbufsize + sc->cachelsz - 1);
> + return NULL;
> + }
> + /*
> + * Cache-line-align. This is important (for the
> + * 5210 at least) as not doing so causes bogus data
> + * in rx'd frames.
> + */
> + off = ((unsigned long)skb->data) % sc->cachelsz;
> + if (off != 0)
> + skb_reserve(skb, sc->cachelsz - off);
> +
> + *skb_addr = pci_map_single(sc->pdev,
> + skb->data, sc->rxbufsize, PCI_DMA_FROMDEVICE);
> + if (unlikely(pci_dma_mapping_error(sc->pdev, *skb_addr))) {
> + ATH5K_ERR(sc, "%s: DMA mapping failed\n", __func__);
> + dev_kfree_skb(skb);
> + return NULL;
> + }
> + return skb;
> +}
> +
> static int
> ath5k_rxbuf_setup(struct ath5k_softc *sc, struct ath5k_buf *bf)
> {
> @@ -1102,37 +1138,11 @@ ath5k_rxbuf_setup(struct ath5k_softc *sc, struct ath5k_buf *bf)
> struct sk_buff *skb = bf->skb;
> struct ath5k_desc *ds;
>
> - if (likely(skb == NULL)) {
> - unsigned int off;
> -
> - /*
> - * Allocate buffer with headroom_needed space for the
> - * fake physical layer header at the start.
> - */
> - skb = dev_alloc_skb(sc->rxbufsize + sc->cachelsz - 1);
> - if (unlikely(skb == NULL)) {
> - ATH5K_ERR(sc, "can't alloc skbuff of size %u\n",
> - sc->rxbufsize + sc->cachelsz - 1);
> + if (!skb) {
> + skb = ath5k_rx_skb_alloc(sc, &bf->skbaddr);
> + if (!skb)
> return -ENOMEM;
> - }
> - /*
> - * Cache-line-align. This is important (for the
> - * 5210 at least) as not doing so causes bogus data
> - * in rx'd frames.
> - */
> - off = ((unsigned long)skb->data) % sc->cachelsz;
> - if (off != 0)
> - skb_reserve(skb, sc->cachelsz - off);
> -
> bf->skb = skb;
> - bf->skbaddr = pci_map_single(sc->pdev,
> - skb->data, sc->rxbufsize, PCI_DMA_FROMDEVICE);
> - if (unlikely(pci_dma_mapping_error(sc->pdev, bf->skbaddr))) {
> - ATH5K_ERR(sc, "%s: DMA mapping failed\n", __func__);
> - dev_kfree_skb(skb);
> - bf->skb = NULL;
> - return -ENOMEM;
> - }
> }
>
> /*
> @@ -1661,7 +1671,8 @@ ath5k_tasklet_rx(unsigned long data)
> {
> struct ieee80211_rx_status rxs = {};
> struct ath5k_rx_status rs = {};
> - struct sk_buff *skb;
> + struct sk_buff *skb, *next_skb;
> + dma_addr_t next_skb_addr;
> struct ath5k_softc *sc = (void *)data;
> struct ath5k_buf *bf, *bf_last;
> struct ath5k_desc *ds;
> @@ -1746,10 +1757,17 @@ ath5k_tasklet_rx(unsigned long data)
> goto next;
> }
> accept:
> + next_skb = ath5k_rx_skb_alloc(sc, &next_skb_addr);
> +
> + /*
> + * If we can't replace bf->skb with a new skb under memory
> + * pressure, just skip this packet
> + */
> + if (!next_skb)
> + goto next;
> +
> pci_unmap_single(sc->pdev, bf->skbaddr, sc->rxbufsize,
> PCI_DMA_FROMDEVICE);
> - bf->skb = NULL;
> -
> skb_put(skb, rs.rs_datalen);
>
> /* The MAC header is padded to have 32-bit boundary if the
> @@ -1822,6 +1840,9 @@ accept:
> ath5k_check_ibss_tsf(sc, skb, &rxs);
>
> __ieee80211_rx(sc->hw, skb, &rxs);
> +
> + bf->skb = next_skb;
> + bf->skbaddr = next_skb_addr;
> next:
> list_move_tail(&bf->list, &sc->rxbuf);
> } while (ath5k_rxbuf_setup(sc, bf) == 0);
> --
> 1.6.0.6
>
>
> --
> Bob Copeland %% www.bobcopeland.com
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