[alsa-devel] [PATCH] ALSA: hda: Abort capability probe at invalid register read

[Takashi Iwai]

On Wed, 18 Oct 2017 05:24:16 +0200,
Vinod Koul wrote:
> 
> On Tue, Oct 17, 2017 at 07:15:08PM +0200, Takashi Iwai wrote:
> > On Tue, 17 Oct 2017 19:15:08 +0200,
> > Vinod Koul wrote:
> > > 
> > > On Tue, Oct 17, 2017 at 04:47:11PM +0200, Takashi Iwai wrote:
> > > > The loop in snd_hdac_bus_parse_capabilities() may go to nirvana when
> > > > it hits an invalid register value read:
> > > > 
> > > >  BUG: unable to handle kernel paging request at ffffad5dc41f3fff
> > > >  IP: pci_azx_readl+0x5/0x10 [snd_hda_intel]
> > > >  Call Trace:
> > > >   snd_hdac_bus_parse_capabilities+0x3c/0x1f0 [snd_hda_core]
> > > >   azx_probe_continue+0x7d5/0x940 [snd_hda_intel]
> > > >   .....
> > > > 
> > > > This happened on a new Intel machine, and we need to check the value
> > > > and abort the loop accordingly.
> > > 
> > > okay and what machine is the problem here. I have had a similar bug report
> > > from Gfx CI guys on  CFL machine. Turns out the BIOS was buggy and we fixed
> > > that up by upgrading the BIOS.
> > 
> > Yes, it's a CFL-H.  Possibly a buggy BIOS, but the driver still
> > shouldn't crash.
> 
> Okay so can you ask them to update BIOS and check.
> 
> > > Yes it is a good idea to keep this guard but -1 would mean that HW read is
> > > failing which points to some other issue here
> > 
> > Right.
> 
> In this case should we send this to stable? I have not seen this crashing
> till now except bad BIOS issue

People will be getting test hardware now and see the Oops.
We can't guarantee the sane BIOS, and obviously the current code does
crash easily, and yet the code fix is trivial -- a perfect situation
for stable :)


Takashi