CVS commit: src/sys/dev/audio

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

Module Name:    src
Committed By:   riastradh
Date:           Sun Oct 10 11:20:29 UTC 2021

Modified Files:
        src/sys/dev/audio: audio.c

Log Message:
audio(9): Call hw_if->getdev without sc_lock.

Holding sc_lock is not necessary -- I reviewed all ~70 cases in-tree,
and none of them rely on state protected by sc_lock.  Essentially
everything just copies from static data or data initialized at attach
time.

(Exceptions: tms320av110.c issues a bus_space_read_1, but I don't see
any reason why that needs to be serialized; and uaudio.c reads from
sc_dying, but that's not necessary and also not protected by sc_lock
anyway.)

Holding sc_lock is harmful because at least hdafg(4) can trigger module
autoload that leads to pserialize_perform, which waits for logic to run
at softint serial on all CPUs; at the same time, audio_softintr_rd/wr
run at softint serial and take sc_lock, so this leads to deadlock.


To generate a diff of this commit:
cvs rdiff -u -r1.108 -r1.109 src/sys/dev/audio/audio.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.