On 2010-12-03 9:14 AM, Ben Greear wrote: > On 12/01/2010 03:22 PM, Ben Greear wrote: >> On 11/29/2010 04:44 PM, Luis R. Rodriguez wrote: >>> On Mon, Nov 29, 2010 at 04:28:51PM -0800, Ben Greear wrote: >> >>>> BUG: unable to handle kernel NULL pointer dereference at 00000040 >>>> IP: [<f933470a>] ath_tx_start+0x461/0x5ef [ath9k] >>>> *pde = 00000000 >>>> Oops: 0000 [#1] SMP DEBUG_PAGEALLOC >>>> last sysfs file: /sys/devices/pci0000:00/0000:00:1e.0/0000:08:01.0/irq >>>> Modules linked in: aes_i586 aes_generic fuse nfs lockd fscache nfs_acl auth_rpcgss sunrpc ipv6 uinput arc4 ecb ath9k mac80211 ath9k_common ath9k_hw mi] >>>> >>>> Pid: 38, comm: kworker/u:1 Tainted: G W 2.6.37-rc3-wl+ #53 PDSBM/PDSBM >>>> EIP: 0060:[<f933470a>] EFLAGS: 00010246 CPU: 1 >>>> EIP is at ath_tx_start+0x461/0x5ef [ath9k] >>> >>> Please use >>> >>> gdb drivers/net/wireless/ath/ath9k/ >>> l *(ath_tx_start+0x461) >>> >>> Luis >> >> I managed to hit that ath_tx_start crash again, and this time there were no obvious >> DMA or irq errors immediately preceding it. So, it might be a real bug >> after all. I'll add some extra checks to see if tid->ac is NULL. > > I've made some small progress on this general issue. > > First, I added all sorts of debugging to try to figure out ath_tx_start crash. > As best as I can tell, 'tid' is not NULL, but also is not a valid pointer, > and probably something close to 0x0. I've added yet more debugging, but haven't > hit the problem again. > > I also tried stopping DMA in a loop up to 5 times if it failed to stop > previously in the loop. This did not appear to help at all. > > I also managed to make both the ath_tx_start crash and the DMA errors very hard to reproduce > (I dare not say fixed, yet). > > It appears that this small patch (and possibly, the fact that I set debugging to 0x600 > instead of 0x400) makes the problems go away. This makes me wonder if a root cause is > something to do with repeatedly resetting the hardware too fast, as setting channels rapidly > would tend to do that, and channels are set on association by supplicant, it appears. Please try this patch while leaving the unnecessary resets in place. I found that when ath_drain_all_txq finds tx dma not stopped, it will issue a reset at a point in time where it is both useless (since it's right before a reset anyway) and dangerous (since the rx dma engine isn't even disabled yet), so IMHO the right thing to do is to drop this extra reset. --- a/drivers/net/wireless/ath/ath9k/xmit.c +++ b/drivers/net/wireless/ath/ath9k/xmit.c @@ -1194,18 +1194,8 @@ void ath_drain_all_txq(struct ath_softc } } - if (npend) { - int r; - - ath_print(common, ATH_DBG_FATAL, - "Failed to stop TX DMA. Resetting hardware!\n"); - - r = ath9k_hw_reset(ah, sc->sc_ah->curchan, ah->caldata, false); - if (r) - ath_print(common, ATH_DBG_FATAL, - "Unable to reset hardware; reset status %d\n", - r); - } + if (npend) + ath_print(common, ATH_DBG_FATAL, "Failed to stop TX DMA!\n"); for (i = 0; i < ATH9K_NUM_TX_QUEUES; i++) { if (ATH_TXQ_SETUP(sc, i)) -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html