When a channel is closed, dsp_close() either calls vchan_destroy() on vchans,
or chn_abort()/chn_flush() on primary channels. However, the problem with this
is that, when closing a vchan, we end up not terminating the stream properly.
The call sequence we are interested in is the following:
vchan_destroy(vchan) -> chn_kill(vchan) -> chn_trigger(vchan) ->
vchan_trigger(vchan) -> chn_notify(parent)
Even though chn_notify() contains codepaths which call chn_abort(parent),
apparently we do not execute any of those codepaths in this case, so the
DMA remains unterminated, hence why we keep seeing the primary
channel(s) being interrupted even once the application has exited:
root@freebsd:~ # sndctl interrupts
dsp0.play.0.interrupts=1139
dsp0.record.0.interrupts=0
root@freebsd:~ # sndctl interrupts
dsp0.play.0.interrupts=1277
dsp0.record.0.interrupts=0
root@freebsd:~ # sndctl interrupts
dsp0.play.0.interrupts=1394
dsp0.record.0.interrupts=0
The only applications that do not have this issue are those (e.g., mpv) that
manually call ioctls which end up calling chn_abort(), like SNDCTL_DSP_HALT, to
abort the channel(s) during shutdown. For all other applications that do not
manually abort the channel(s), we can confirm that chn_abort()/chn_flush(), or
even chn_trigger(PCMTRIG_ABORT) on the parent, doesn't happen during shutdown.
root@freebsd:~ # dtrace -n 'fbt::chn_abort:entry,fbt::chn_flush:entry { printf("%s", args[0]->name); stack(); }'
dtrace: description 'fbt::chn_abort:entry,fbt::chn_flush:entry ' matched 2 probes
dtrace: buffer size lowered to 1m
^C
[...]
root@freebsd:~ # dtrace -n 'fbt::chn_trigger:entry /args[1] == -1/ { printf("%s", args[0]->name); stack(); }'
dtrace: description 'fbt::chn_trigger:entry ' matched 1 probe
dtrace: buffer size lowered to 1m
CPU ID FUNCTION:NAME
0 68037 chn_trigger:entry dsp0.virtual_play.0
sound.ko`chn_kill+0x134
sound.ko`vchan_destroy+0x94
sound.ko`dsp_close+0x39b
kernel`devfs_destroy_cdevpriv+0xab
kernel`devfs_close_f+0x63
kernel`_fdrop+0x1a
kernel`closef+0x1e3
kernel`closefp_impl+0x76
kernel`amd64_syscall+0x151
kernel`0xffffffff8103841b1
To fix this, modify dsp_close() to execute the primary channel case on both
primary and virtual channels. While what we really care about are the
chn_abort()/chn_flush() calls, it shouldn't hurt to call the rest of the
functions on the vchans as well, to avoid complicating things; they get deleted
right below, anyway.
With the patch applied:
root@freebsd:~ # dtrace -n 'fbt::chn_trigger:entry /args[1] == -1/ { printf("%s", args[0]->name); stack(); }'
dtrace: description 'fbt::chn_trigger:entry ' matched 1 probe
dtrace: buffer size lowered to 1m
CPU ID FUNCTION:NAME
1 68037 chn_trigger:entry dsp0.virtual_play.0
sound.ko`chn_flush+0x2a
sound.ko`dsp_close+0x330
kernel`devfs_destroy_cdevpriv+0xab
kernel`devfs_close_f+0x63
kernel`_fdrop+0x1a
kernel`closef+0x1e3
kernel`closefp_impl+0x76
kernel`amd64_syscall+0x151
kernel`0xffffffff8103841b
0 68037 chn_trigger:entry dsp0.play.0
sound.ko`chn_notify+0x4ce
sound.ko`vchan_trigger+0x105
sound.ko`chn_trigger+0xb4
sound.ko`chn_flush+0x2a
sound.ko`dsp_close+0x330
kernel`devfs_destroy_cdevpriv+0xab
kernel`devfs_close_f+0x63
kernel`_fdrop+0x1a
kernel`closef+0x1e3
kernel`closefp_impl+0x76
kernel`amd64_syscall+0x151
kernel`0xffffffff8103841b
Above we can see a chn_trigger(PCMTRIG_ABORT) on the parent (dsp0.play.0),
which is coming from the chn_abort() (inlined) in chn_notify():
root@freebsd:~ # dtrace -n 'kinst::chn_abort:entry { stack(); }'
dtrace: description 'kinst::chn_abort:entry ' matched 5 probes
dtrace: buffer size lowered to 1m
CPU ID FUNCTION:NAME
1 72580 chn_notify:1192
sound.ko`0xffffffff8296cab4
sound.ko`vchan_trigger+0x105
sound.ko`chn_trigger+0xb4
sound.ko`chn_flush+0x2a
sound.ko`dsp_close+0x330
kernel`devfs_destroy_cdevpriv+0xab
kernel`devfs_close_f+0x63
kernel`_fdrop+0x1a
kernel`closef+0x1e3
kernel`closefp_impl+0x76
kernel`amd64_syscall+0x151
kernel`0xffffffff8103841b
We can also confirm the primary channel(s) are not interrupted anymore:
root@freebsd:/mnt/src # sndctl interrupts
dsp0.play.0.interrupts=0
dsp0.record.0.interrupts=0
In collaboration with: adrian
Sponsored by: The FreeBSD Foundation
MFC after: 2 days