On Fri, 31 May 2019 15:52:27 +0200, Ranjani Sridharan wrote:
On Fri, 2019-05-31 at 15:25 +0200, Takashi Iwai wrote:
On Fri, 31 May 2019 15:18:03 +0200, Ranjani Sridharan wrote:
On Fri, 2019-05-31 at 08:11 +0200, Takashi Iwai wrote:
On Thu, 30 May 2019 23:00:10 +0200, Pierre-Louis Bossart wrote:
On 5/30/19 3:18 PM, Ranjani Sridharan wrote:
Calling snd_device_new() makes the codec devices managed by the card. So, when the card is removed, the refcount for the codec device is decremented and results in the codec device's kobject being cleaned up if the refcount is 0. But, this leads to a NULL pointer exception while attempting to remove the symlinks when the codec driver is released later on. Therefore, increment the codec device's refcount before adding it to the card to prevent this.
Ranjani, you should add a bit of context for the rest of the list...
This patch suggest a solution to a set of sightings occurring when removing/adding modules in a loop, and the current analysis points to a difference between the way the HDMI and HDaudio codecs are handled.
https://github.com/thesofproject/linux/issues/981 https://github.com/thesofproject/linux/issues/966 https://github.com/thesofproject/linux/pull/988
Since it's not SOF specific it's better to get feedback directly from the large ALSA community/maintainers. We probably want to focus on the platform-specific/vendor-specific stuff on GitHub and use the mailing list for such framework-level changes.
Hm, I still wonder why this doens't happen with the HDA legacy.
What is the shortest way to trigger the bug manually without a script?
Hi Takashi,
With SOF, I can reproduce the issue if I just unload the sof_pci_dev module with rmmod.
Basically, the remove routine for the SOF pci device, unregisters the machine driver and then removes the codec device. So the first step of unregistering the machine driver frees the card which decrements the refcount for the HDA codec's kobject. In the case of HDMI codec, since it is not managed by the card, the refcount is not decremented when the card is removed.
So it's only about hdac_hdmi codec, or only about hdac_hda codec?
It is only about the hdac_hda codec.
And why HDMI codec isn't managed by the card...? IOW, isn't it dangerous -- it means the codec being always removable after bound to the card?
That is a good point. Probably this needs to be fixed as well. I can include the change for that if you think it is the right thing to do.
But I was wondering if it makes sense to increment the refcount when the device is added to the card with snd_device_new()? I'm not sure how it affects the other devices so didnt go down this route.
If you mean really snd_device_new() calls generically, not specific to snd_hda_codec_device_new() -- then no, something must be wrong.
And even for snd_hda_codec_device_new(), I'm not sure about it.
Actually, who decrements the device refcount at which timing...? It'd be helpful if you can clarify it, then we might see a better solution or a better explanation.
thanks,
Takashi