Date:   Tue, 30 Apr 2019 12:17:35 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Liwei Song <liwei.song@...driver.com>
Cc:     <alsa-devel@...a-project.org>, Yu Zhao <yuzhao@...gle.com>,
        Mark Brown <broonie@...nel.org>,
        Keyon Jie <yang.jie@...ux.intel.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: hda: check RIRB to avoid use NULL pointer

On Tue, 30 Apr 2019 11:29:19 +0200,
Liwei Song wrote:
> 
> 
> 
> On 04/30/2019 04:53 PM, Takashi Iwai wrote:
> > On Tue, 30 Apr 2019 10:32:47 +0200,
> > Liwei Song wrote:
> >>
> >>
> >>
> >> On 04/30/2019 03:31 PM, Takashi Iwai wrote:
> >>> On Tue, 30 Apr 2019 08:10:53 +0200,
> >>> Song liwei wrote:
> >>>>
> >>>> From: Liwei Song <liwei.song@...driver.com>
> >>>>
> >>>> Fix the following BUG:
> >>>>
> >>>> BUG: unable to handle kernel NULL pointer dereference at 000000000000000c
> >>>> Workqueue: events azx_probe_work [snd_hda_intel]
> >>>> RIP: 0010:snd_hdac_bus_update_rirb+0x80/0x160 [snd_hda_core]
> >>>> Call Trace:
> >>>>  <IRQ>
> >>>>  azx_interrupt+0x78/0x140 [snd_hda_codec]
> >>>>  __handle_irq_event_percpu+0x49/0x300
> >>>>  handle_irq_event_percpu+0x23/0x60
> >>>>  handle_irq_event+0x3c/0x60
> >>>>  handle_edge_irq+0xdb/0x180
> >>>>  handle_irq+0x23/0x30
> >>>>  do_IRQ+0x6a/0x140
> >>>>  common_interrupt+0xf/0xf
> >>>>
> >>>> The Call Trace happened when run kdump on a NFS rootfs system.
> >>>> Exist the following calling sequence when boot the second kernel:
> >>>>
> >>>> azx_first_init()
> >>>>    --> azx_acquire_irq()
> >>>>                       <-- interrupt come in, azx_interrupt() was called
> >>>>    --> hda_intel_init_chip()
> >>>>       --> azx_init_chip()
> >>>>          --> snd_hdac_bus_init_chip()
> >>>>               --> snd_hdac_bus_init_cmd_io();
> >>>>                     --> init rirb.buf and corb.buf
> >>>>
> >>>> Interrupt happened after azx_acquire_irq() while RIRB still didn't got
> >>>> initialized, then NULL pointer will be used when process the interrupt.
> >>>>
> >>>> Check the value of RIRB to ensure it is not NULL, to aviod some special
> >>>> case may hang the system.
> >>>>
> >>>> Fixes: 14752412721c ("ALSA: hda - Add the controller helper codes to hda-core module")
> >>>> Signed-off-by: Liwei Song <liwei.song@...driver.com>
> >>>
> >>> Oh, that's indeed a race there.
> >>>
> >>> But I guess the check introduced by the patch is still error-prone.
> >>> Basically the interrupt handling should be moved after the chip
> >>> initialization.  I suppose that your platform uses the shared
> >>> interrupt, not the MSI?
> >>
> >> This is the information from /proc/interrupt
> >> 134:          0        102          0          0  IR-PCI-MSI 514048-edge      snd_hda_intel:card0
> > 
> > Hm, then it's interesting...
> > 
> > 
> >>> In anyway, alternative (and likely more certain) fix would be to move
> >>> the azx_acquir_irq() call like the patch below (note: totally
> >>> untested).  Could you check whether it works?
> >>
> >> Yes, It works.
> >>
> >> Considering a previous patch like the one you provide will import some issue, 
> >> so I choose check the invalid value to low the risk, but just as you mentioned,
> >> It is not a good solution.
> >>
> >> commit 542cedec53c9e8b73f3f05bf8468823598c50489
> >> Author: Yu Zhao <yuzhao@...gle.com>
> >> Date:   Tue Sep 11 15:12:46 2018 -0600
> >>
> >>     Revert "ASoC: Intel: Skylake: Acquire irq after RIRB allocation"
> >>     
> >>     This reverts commit 12eeeb4f4733bbc4481d01df35933fc15beb8b19.
> >>     
> >>     The patch doesn't fix accessing memory with null pointer in
> >>     skl_interrupt().
> >>     
> >>     There are two problems: 1) skl_init_chip() is called twice, before
> >>     and after dma buffer is allocate. The first call sets bus->chip_init
> >>     which prevents the second from initializing bus->corb.buf and
> >>     rirb.buf from bus->rb.area. 2) snd_hdac_bus_init_chip() enables
> >>     interrupt before snd_hdac_bus_init_cmd_io() initializing dma buffers.
> >>     There is a small window which skl_interrupt() can be called if irq
> >>     has been acquired. If so, it crashes when using null dma buffer
> >>     pointers.
> > 
> > Actually this followed by another fix b61749a89f82,
> >     sound: enable interrupt after dma buffer initialization
> >     
> > and this moved the IRQ enablement after snd_hdac_bus_init_cmd_io().
> > 
> > So I wonder how the irq gets triggered in your case.
> > If it were a shared irq, it's understandable.  But for MSI, it should
> > have been the isolated source.
> 
> I'm still working on how the irq was triggered,
> it is a little complex to reproduce it, first it must run with NFS rootfs,
> without NFS rootfs it can not reproduced.
> Then with kdump enabled, after "echo c > /proc/sysrq-trigger" crash the kernel,
> the kernel specified by kdump will boot, then interrupt will trigger
> soon after azx interrupt was register.

Ah, so it happens in a kdump kernel?  It implies that the interrupt
line may be still active (or confused).  Then it's no wonder a stale
interrupt comes up.

> > In anyway, for the latest tree, the change I suggested would cover
> > better although it's more radical as you pointed.
> 
> Got it, Thanks.

OK, I'm going to submit and apply the proper patch.


thanks,

Takashi

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