Re: [PATCH] ALSA: hda: Abort capability probe at invalid register read

[Vinod Koul <vinod.koul@intel.com>]

On Wed, Oct 18, 2017 at 07:42:12AM +0200, Takashi Iwai wrote:
> 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 :)

Right :), But do make sure to ask for BIOS update on that board.

Acked-By: Vinod Koul <vinod.koul@intel.com>

-- 
~Vinod