This patchset serves to prevent a deadlock between
process context and softIRQ context:
A. In the process context
* (lock A) Acquiring spin_lock by snd_pcm_stream_lock_irq() in
snd_pcm_status64()
* (lock B) Then attempt to enter tasklet
B. In the softIRQ context
* (lock B) Enter tasklet
* (lock A) Attempt to acquire spin_lock by snd_pcm_stream_lock_irqsave() in
snd_pcm_period_elapsed()
? tasklet_unlock_spin_wait
</NMI>
<TASK>
ohci_flush_iso_completions firewire_ohci
amdtp_domain_stream_pcm_pointer snd_firewire_lib
snd_pcm_update_hw_ptr0 snd_pcm
snd_pcm_status64 snd_pcm
? native_queued_spin_lock_slowpath
</NMI>
<IRQ>
_raw_spin_lock_irqsave
snd_pcm_period_elapsed snd_pcm
process_rx_packets snd_firewire_lib
irq_target_callback snd_firewire_lib
handle_it_packet firewire_ohci
context_tasklet firewire_ohci
The issue has been reported as a regression of kernel 5.14:
Link: https://lore.kernel.org/regressions/kwryofzdmjvzkuw6j3clftsxmoolynljztxqwg76hzeo4simnl@jn3eo7pe642q/T/#u
("[REGRESSION] ALSA: firewire-lib: snd_pcm_period_elapsed deadlock with
Fireface 800")
Commit 7ba5ca32fe6e ("ALSA: firewire-lib: operate for period elapse event
in process context") removed the process context workqueue from
amdtp_domain_stream_pcm_pointer() and update_pcm_pointers() to remove
its overhead.
Commit b5b519965c4c ("ALSA: firewire-lib: obsolete workqueue for period
update") belongs to the same patch series and removed
the now-unused workqueue entirely.
Though being observed on RME Fireface 800, this issue would affect all
Firewire audio interfaces using ohci amdtp + pcm streaming.
ALSA streaming, especially under intensive CPU load will reveal this issue
the soonest due to issuing more hardIRQs, with time to occurrence ranging
from 2 secons to 30 minutes after starting playback.
to reproduce the issue:
direct ALSA playback to the device:
mpv --audio-device=alsa/sysdefault:CARD=Fireface800 Spor-Ignition.flac
Time to occurrence: 2s to 30m
Likelihood increased by:
- high CPU load
stress --cpu $(nproc)
- switching between applications via workspaces
tested with i915 in Xfce
PulsaAudio / PipeWire conceal the issue as they run PCM substream
without period wakeup mode, issuing less hardIRQs.
Backport note:
Also applies to and fixes on (tested):
6.10.2, 6.9.12, 6.6.43, 6.1.102, 5.15.164
Edmund Raile (2):
ALSA: firewire-lib: restore workqueue for process context
ALSA: firewire-lib: prevent deadlock between process and softIRQ
context
sound/firewire/amdtp-stream.c | 36 ++++++++++++++++++++++-------------
sound/firewire/amdtp-stream.h | 1 +
2 files changed, 24 insertions(+), 13 deletions(-)
--
2.45.2
