Re: [PATCH] ath10k: fix kernel panic while shutting down AP

From: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
To: Michal Kazior <michal.kazior@tieto.com>
Cc: linux-wireless <linux-wireless@vger.kernel.org>,
	"ath10k@lists.infradead.org" <ath10k@lists.infradead.org>
Subject: Re: [PATCH] ath10k: fix kernel panic while shutting down AP
Date: Wed, 8 Oct 2014 16:03:15 +0530	[thread overview]
Message-ID: <20141008103312.GA25666@qca.qualcomm.com> (raw)
In-Reply-To: <CA+BoTQ=K=F5TodrmuaEaJfErFx1=BL-bmPDrAaeMLjjb8c3fJQ@mail.gmail.com>

On Wed, Oct 08, 2014 at 11:45:38AM +0200, Michal Kazior wrote:
> On 8 October 2014 11:16, Rajkumar Manoharan <rmanohar@qti.qualcomm.com> 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.

Similar to dma_alloc_coherent, dma_free_coherent can not be called under
soft irq context.

PS: I am using upstream ath10k driver without private changes.

-Rajkumar

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