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Date:   Tue, 09 Jun 2020 10:05:26 +0200
Message-ID: <s5hsgf4irzt.wl-tiwai@suse.de>
From:   Takashi Iwai <tiwai@suse.de>
To:     Christoph Hellwig <hch@lst.de>
Cc:     David Rientjes <rientjes@google.com>,
        "Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>,
        <alsa-devel@alsa-project.org>, <bp@alien8.de>, <hch@infradead.org>,
        <hpa@zytor.com>, <linux-kernel@vger.kernel.org>,
        <mingo@redhat.com>, Pavel Machek <pavel@ucw.cz>, <perex@perex.cz>,
        <tglx@linutronix.de>, <tiwai@suse.com>, <x86@kernel.org>
Subject: Re: next-0519 on thinkpad x60: sound related? window manager crash
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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