Date: Thu, 29 May 2025 22:10:08 GMT From: Christos Margiolis <christos@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 0c6aa445ec0c - stable/14 - sound: Terminate stream properly when closing vchans Message-ID: <202505292210.54TMA8Nf079371@gitrepo.freebsd.org>
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The branch stable/14 has been updated by christos: URL: https://cgit.FreeBSD.org/src/commit/?id=0c6aa445ec0c85e7c9653d20562907742569de6f commit 0c6aa445ec0c85e7c9653d20562907742569de6f Author: Christos Margiolis <christos@FreeBSD.org> AuthorDate: 2025-05-29 10:24:17 +0000 Commit: Christos Margiolis <christos@FreeBSD.org> CommitDate: 2025-05-29 22:09:40 +0000 sound: Terminate stream properly when closing vchans 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 Tested by: adrian, christos, thj Sponsored by: The FreeBSD Foundation MFC after: 2 days Reviewed by: thj, adrian, emaste Differential Revision: https://reviews.freebsd.org/D50488 (cherry picked from commit f6430bc61df78be070209d52b4452ae9cf4cd015) --- sys/dev/sound/pcm/dsp.c | 33 +++++++++++++++++++-------------- 1 file changed, 19 insertions(+), 14 deletions(-) diff --git a/sys/dev/sound/pcm/dsp.c b/sys/dev/sound/pcm/dsp.c index f1adcdbc5d70..aa6ad4a59778 100644 --- a/sys/dev/sound/pcm/dsp.c +++ b/sys/dev/sound/pcm/dsp.c @@ -289,19 +289,25 @@ dsp_close(void *data) if (sg_ids != 0) free_unr(pcmsg_unrhdr, sg_ids); + /* + * Go through the channel abort/flush path for both + * primary and virtual channels to ensure that, in the + * case of vchans, the stream is always properly + * stopped, and the primary channels do not keep being + * interrupted even if all vchans are gone. + */ + CHN_LOCK(rdch); + chn_abort(rdch); /* won't sleep */ + rdch->flags &= ~(CHN_F_RUNNING | CHN_F_MMAP | + CHN_F_DEAD | CHN_F_EXCLUSIVE); + chn_reset(rdch, 0, 0); + chn_release(rdch); if (rdch->flags & CHN_F_VIRTUAL) { parent = rdch->parentchannel; CHN_LOCK(parent); CHN_LOCK(rdch); vchan_destroy(rdch); CHN_UNLOCK(parent); - } else { - CHN_LOCK(rdch); - chn_abort(rdch); /* won't sleep */ - rdch->flags &= ~(CHN_F_RUNNING | CHN_F_MMAP | - CHN_F_DEAD | CHN_F_EXCLUSIVE); - chn_reset(rdch, 0, 0); - chn_release(rdch); } } if (wrch != NULL) { @@ -314,19 +320,18 @@ dsp_close(void *data) if (sg_ids != 0) free_unr(pcmsg_unrhdr, sg_ids); + CHN_LOCK(wrch); + chn_flush(wrch); /* may sleep */ + wrch->flags &= ~(CHN_F_RUNNING | CHN_F_MMAP | + CHN_F_DEAD | CHN_F_EXCLUSIVE); + chn_reset(wrch, 0, 0); + chn_release(wrch); if (wrch->flags & CHN_F_VIRTUAL) { parent = wrch->parentchannel; CHN_LOCK(parent); CHN_LOCK(wrch); vchan_destroy(wrch); CHN_UNLOCK(parent); - } else { - CHN_LOCK(wrch); - chn_flush(wrch); /* may sleep */ - wrch->flags &= ~(CHN_F_RUNNING | CHN_F_MMAP | - CHN_F_DEAD | CHN_F_EXCLUSIVE); - chn_reset(wrch, 0, 0); - chn_release(wrch); } } PCM_LOCK(d);
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