Re: next-0519 on thinkpad x60: sound related? window manager crash

Takashi Iwai
2020-06-09T08:06:33Z

On Tue, 09 Jun 2020 07:43:06 +0200,
Christoph Hellwig wrote:
>
> On Mon, Jun 08, 2020 at 07:31:47PM -0700, David Rientjes wrote:
> > On Mon, 8 Jun 2020, Alex Xu (Hello71) wrote:
> >
> > > Excerpts from Christoph Hellwig's message of June 8, 2020 2:19 am:
> > > > Can you do a listing using gdb where this happens?
> > > >
> > > > gdb vmlinux
> > > >
> > > > l *(snd_pcm_hw_params+0x3f3)
> > > >
> > > > ?
> > > >
> > >
> > > (gdb) l *(snd_pcm_hw_params+0x3f3)
> > > 0xffffffff817efc85 is in snd_pcm_hw_params (.../linux/sound/core/pcm_native.c:749).
> > > 744 while (runtime->boundary * 2 <= LONG_MAX - runtime->buffer_size)
> > > 745 runtime->boundary *= 2;
> > > 746
> > > 747 /* clear the buffer for avoiding possible kernel info leaks */
> > > 748 if (runtime->dma_area && !substream->ops->copy_user)
> > > 749 memset(runtime->dma_area, 0, runtime->dma_bytes);
> > > 750
> > > 751 snd_pcm_timer_resolution_change(substream);
> > > 752 snd_pcm_set_state(substream, SNDRV_PCM_STATE_SETUP);
> > > 753
> > >
> >
> > Working theory is that CONFIG_DMA_NONCOHERENT_MMAP getting set is causing
> > the error_code in the page fault path. Debugging with Alex off-thread we
> > found that dma_{alloc,free}_from_pool() are not getting called from the
> > new code in dma_direct_{alloc,free}_pages() and he has not enabled
> > mem_encrypt.
>
> While DMA_COHERENT_POOL absolutely should not select DMA_NONCOHERENT_MMAP
> (and you should send your patch either way), I don't think it is going
> to make a difference here, as DMA_NONCOHERENT_MMAP just means we
> allows mmaps even for non-coherent devices, and we do not support
> non-coherent devices on x86.
>
> >From the disassembly it seems like a vmalloc allocation is NULL, which
> seems really weird as this patch shouldn't make a difference for them,
> and I also only see a single places that allocates the field, and that
> checks for an allocation failure. But the sound code is a little
> hard to unwind sometimes.

It's not clear which sound device being affected, but if it's
HD-audio on x86, runtime->dma_area points to a vmapped buffer from
SG-pages allocated by dma_alloc_coherent().

OTOH, if it's a USB-audio, runtime->dma_area is a buffer by
vmalloc().

Takashi