Re: [PATCH] ASoC: soc-core: Fix null pointer dereference in soc_find_component

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The issue was that we were seeing a memory corruption bug on an AMD
chromebooks with that function already (not observed on Intel). I was
testing some SOF integrations and was seeing this in the kernel logs.
I had Dylan verify my logic before I sent the patch because it took so
long to identify the bug and it was traced to the patch that introduce
soc_init_platform.

[   10.922112] cz-da7219-max98357a AMD7219:00: ASoC: CPU DAI
designware-i2s.1.auto not registered
[   10.922122] cz-da7219-max98357a AMD7219:00:
devm_snd_soc_register_card(acpd7219m98357) failed: -517
[   11.001411] cz-da7219-max98357a AMD7219:00: ASoC: Both platform
name/of_node are set for amd-max98357-play
[   11.001423] cz-da7219-max98357a AMD7219:00: ASoC: failed to init
link amd-max98357-play
[   11.001431] cz-da7219-max98357a AMD7219:00:
devm_snd_soc_register_card(acpd7219m98357) failed: -22
[   11.001577] cz-da7219-max98357a: probe of AMD7219:00 failed with error -22

of_node was never getting set but the pointer was becoming populated
(outside of the probe call) which traced to soc_init_platform function
which was not reallocating memory on a EPROBE_DEFER even though it was
getting freed by devm. I am not very familiar with devm but my local
maintainers say that it should be freeing the memory even on a
PROBE_DEFER.
The patch should mirror the memory behaviour in
snd_soc_init_multicodec which also reallocates its memory on every
probe. I'm not sure how the patch is causing you to defer, is your
component list corrupt?

Sorry for the duplicate spam, forgot to send via plain text mode,
re-sending for the mailing list so it gets accepted.

There is no defer issue with the intel stuff, but we call this routine multiple times

snd_soc_register_card

--soc_init_dai_link

----snd_soc_init_platform

-- soc_soc_bind_card

----snd_soc_instantiate_card

------ soc_check_tplg_fes

-------- snd_soc_init_platform << ALLOC1

--------soc_init_dai_link

----------snd_soc_init_platform << ALLOC2

Initially dai_link->legacy_platform is 0, so gets set after the first first devm_kzalloc (ALLOC1) and after that we always allocate new memory (ALLOC2). The end result is that whatever we set in soc_check_tplg_fes is lost with the new/unnecessary alloc.

I would guess your solution is also a work-around, if devm_ effectively freed the memory then the pointer would become NULL. Or may that's the issue is that no one actually resets it.



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