On 8 October 2014 13:08, Rajkumar Manoharan <rmanohar@xxxxxxxxxxxxxxxx> wrote: > On Wed, Oct 08, 2014 at 12:50:28PM +0200, Michal Kazior wrote: >> On 8 October 2014 12:33, Rajkumar Manoharan <rmanohar@xxxxxxxxxxxxxxxx> wrote: >> > On Wed, Oct 08, 2014 at 11:45:38AM +0200, Michal Kazior wrote: >> >> On 8 October 2014 11:16, Rajkumar Manoharan <rmanohar@xxxxxxxxxxxxxxxx> wrote: >> >> > The commit "ath10k: workaround fw beaconing bug" is freeing >> >> > DMA-coherent memory in irq context which is hitting BUG ON >> >> > in ARM platforms. Fix this by moving dma_free out of spin >> >> > lock. >> >> >> >> I hardly see how moving the freeing outside the spinlock is a fix. >> >> >> >> >> >> > kernel BUG at mm/vmalloc.c:1512! >> >> > Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM >> >> > CPU: 0 PID: 722 Comm: hostapd Not tainted 3.14.0 #3 >> >> > task: dd58b840 ti: da6a6000 task.ti: da6a6000 >> >> > PC is at vunmap+0x24/0x34 >> >> > LR is at __arm_dma_free.isra.21+0x12c/0x190 >> >> > [<c02a97d0>] (vunmap) from [<c021f81c>] (__arm_dma_free.isra.21+0x12c/0x190) >> >> > [<c021f81c>] (__arm_dma_free.isra.21) from [<bf3b2440>] >> >> > (ath10k_mac_vif_beacon_free+0xf4/0x100 [ath10k_core]) >> >> > [<bf3b2440>] (ath10k_mac_vif_beacon_free [ath10k_core]) from [<bf3b2490>] >> >> > (ath10k_remove_interface+0x44/0x1ec [ath10k_core]) >> >> > [<bf3b2490>] (ath10k_remove_interface [ath10k_core]) from [<bf3352e4>] >> >> > (ieee80211_add_virtual_monitor+0x9d8/0x9f0 [mac80211]) >> >> > [<bf3352e4>] (ieee80211_add_virtual_monitor [mac80211]) from [<bf33530c>] >> >> > (ieee80211_stop+0x10/0x18 [mac80211]) >> >> > [<bf33530c>] (ieee80211_stop [mac80211]) from [<c040d144>] >> >> > (__dev_close_many+0x9c/0xcc) >> >> >> >> 1. How can even ieee80211_add_virtual_monitor() call >> >> ath10k_remove_interface()? Upstream ath10k doesn't advertise >> >> IEEE80211_HW_WANT_MONITOR_VIF. This call trace is either invalid, >> >> you're not using upstream ath10k and/or have custom patches applied to >> >> ath10k. >> >> >> > This is the backtrace captured on panic and we are getting the same >> > backtrace consistently. I confirmed that add_virtual_monitor is not >> > called for ath10k as it is not advertising. ath10k_remove_interface is >> > called for master mode. >> > >> >> 2. How can ieee80211_stop() be called from an interrupt context >> >> anyway? ieee80211_stop() calls ieee80211_do_stop() which calls >> >> ieee80211_roc_purge() which tries to get a hold of local->mtx. This >> >> implies ieee80211_stop() isn't design to be run in an interrupt >> >> context to begin with so I don't see why ath10k should even care if >> >> ath10k_remove_interface() is called in an interrupt context at this >> >> point. >> >> >> > in_interrupt is counting soft and hard irqs. ieee80211_stop is not >> > called from interrupt context. In ath10k, by aquiring spin_lock in >> > ath10k_mac_vif_beacon_free is increasing soft irq count. >> > >> > In ARM arch, __arm_dma_free is calling vunmap which might sleep. So it >> > can not be called within spin_lock. >> >> Did you try using GFP_ATOMIC in the dma_alloc_coherent instead of >> moving the spinlock? >> > Nope. The problem is while freeing dma memory not during allocation. > dma_free_coherent won't take any GFP_* flags. My thinking was GFP_ given to dma_alloc_coherent could impact behaviour of dma_free_coherent (e.g. different kind of pages is allocated so different kind of freeing will be involved) but I may be wrong. Can you give it a try, please? >> > Similar to dma_alloc_coherent, dma_free_coherent can not be called under >> > soft irq context. >> >> The call trace points to ath10k_mac_vif_beacon_free() which doesn't >> use dma_free_coherent() so why are you blaming it for the BUG_ON? >> > I agree the calltrace is a bogus. ath10k_mac_vif_beacon_cleanup is > calling dma_free_coherent. The call trace without additional comment in the commit log (stating the fact that the call trace is inaccurate for some reason) is confusing. >> If anything the offender should be dma_unmap_single() but the thing is >> beacon_buf is always allocated for AP/IBSS now which means >> dma_unmap_single() is never called. For non-AP/IBSS both arvif->beacon >> and arvif->beacon_buf are always NULL so neither >> dma_alloc/free_coherent nor dma_map/unmap_single are called. >> > Agree. We need one more check in ath10k_mac_vif_beacon_free. But here > the problem is dma_free_coherent is being called from soft irq context > which is not allowed (BUG_ON noted in ARM arch). > > After moving dma_free_coherent out of spinlock, the kernel > BUG at mm/vmalloc.c:1512 is never hit. It seems there's a bit of branching in the arm dma code. Maybe it's possible to fix this problem in ath10k differently (vide the gfp idea). Michał -- 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
