ALSA: oss: Keep emulation modules loaded until object teardown

OSS proc entries and notifier callbacks can remain in use without an
open OSS device file. Normal snd-pcm-oss removal can therefore delete
an existing PCM's OSS proc entry while late HDA codec binding repeats
snd_card_register() on the same live card:

  OSS PCM module unload                 Card registration
  ---------------------                 -----------------
  snd_info_free_entry(entry)
    proc_remove(entry->p)
    clear entry->p
                                        snd_info_card_register()
                                          republish linked entry
    unlink and free entry

The new proc node retains a pointer to freed storage. Mixer OSS removal
can likewise release an adapter while a card notification still uses it.

Hold a snd-pcm-oss module reference for each PCM registered with its
notifier and a snd-mixer-oss reference for each card adapter. Release
them at final unregister or FREE, after proc and adapter cleanup. Normal
module unload can no longer initiate removal while these objects exist.

Track PCM OSS registration with a separate bool registered. Unlike
oss.reg, this state also covers unmapped PCMs and remains set across
DISCONNECT until final unregister. BUILD-state and creation-error cleanup
must not drop a reference when registration never acquired one. The PCM
notifier's register_mutex serialization keeps the final put ahead of
notifier removal and module teardown until dispatch has finished.

For mixer OSS, serialize callback publication, dispatch and withdrawal
in the core so module exit waits for callbacks, including one dropping
the last reference, to return. Keep card enumeration in the OSS module,
with card references released after dispatch drops the mutex. Ignore
duplicate REGISTER notifications so a delayed registration cannot
replace an adapter retained across DISCONNECT and leak its module pin.

Partial HDA codec teardown can still remove an individual PCM while the
card remains registered; its object-lifetime handling is separate.

Fixes: 2471b6c80a70 ("ALSA: info: Register proc entries recursively, too")
Suggested-by: Takashi Iwai <tiwai@suse.de>
Assisted-by: LLM
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/pm-pmb-26d66390a25fec9fad6c-v6-5be251a3ac8832955a31-2@gmail.com

0 files changed, 0 insertions, 0 deletions