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

[Christoph Hellwig <hch@lst.de>]

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.