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.
With RME Fireface 800, this lead to a regression since Kernels 5.14.0, causing an AB/BA deadlock competition for the substream lock with eventual system freeze under ALSA operation:
thread 0: * (lock A) acquire substream lock by snd_pcm_stream_lock_irq() in snd_pcm_status64() * (lock B) wait for tasklet to finish by calling tasklet_unlock_spin_wait() in tasklet_disable_in_atomic() in ohci_flush_iso_completions() of ohci.c
thread 1: * (lock B) enter tasklet * (lock A) attempt to acquire substream lock, waiting for it to be released: snd_pcm_stream_lock_irqsave() in snd_pcm_period_elapsed() in update_pcm_pointers() in process_ctx_payloads() in process_rx_packets() of amdtp-stream.c
? 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
Restore the process context work queue to prevent deadlock AB/BA deadlock competition for ALSA substream lock of snd_pcm_stream_lock_irq() in snd_pcm_status64() and snd_pcm_stream_lock_irqsave() in snd_pcm_period_elapsed().
commit 7ba5ca32fe6e ("ALSA: firewire-lib: operate for period elapse event in process context")
Cc: stable@vger.kernel.org Fixes: 7ba5ca32fe6e ("ALSA: firewire-lib: operate for period elapse event in process context") Link: https://lore.kernel.org/r/kwryofzdmjvzkuw6j3clftsxmoolynljztxqwg76hzeo4simnl... Reported-by: edmund.raile edmund.raile@proton.me Closes: https://lore.kernel.org/r/kwryofzdmjvzkuw6j3clftsxmoolynljztxqwg76hzeo4simnl... Signed-off-by: Edmund Raile edmund.raile@protonmail.com --- sound/firewire/amdtp-stream.c | 31 +++++++++++++++++-------------- 1 file changed, 17 insertions(+), 14 deletions(-)
diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c index 31201d506a21..a07b0452267d 100644 --- a/sound/firewire/amdtp-stream.c +++ b/sound/firewire/amdtp-stream.c @@ -615,16 +615,8 @@ static void update_pcm_pointers(struct amdtp_stream *s, // The program in user process should periodically check the status of intermediate // buffer associated to PCM substream to process PCM frames in the buffer, instead // of receiving notification of period elapsed by poll wait. - if (!pcm->runtime->no_period_wakeup) { - if (in_softirq()) { - // In software IRQ context for 1394 OHCI. - snd_pcm_period_elapsed(pcm); - } else { - // In process context of ALSA PCM application under acquired lock of - // PCM substream. - snd_pcm_period_elapsed_under_stream_lock(pcm); - } - } + if (!pcm->runtime->no_period_wakeup) + queue_work(system_highpri_wq, &s->period_work); } }
@@ -1864,11 +1856,22 @@ unsigned long amdtp_domain_stream_pcm_pointer(struct amdtp_domain *d, { struct amdtp_stream *irq_target = d->irq_target;
- // Process isochronous packets queued till recent isochronous cycle to handle PCM frames. if (irq_target && amdtp_stream_running(irq_target)) { - // In software IRQ context, the call causes dead-lock to disable the tasklet - // synchronously. - if (!in_softirq()) + // This function is called in software IRQ context of + // period_work or process context. + // + // When the software IRQ context was scheduled by software IRQ + // context of IT contexts, queued packets were already handled. + // Therefore, no need to flush the queue in buffer furthermore. + // + // When the process context reach here, some packets will be + // already queued in the buffer. These packets should be handled + // immediately to keep better granularity of PCM pointer. + // + // Later, the process context will sometimes schedules software + // IRQ context of the period_work. Then, no need to flush the + // queue by the same reason as described in the above + if (current_work() != &s->period_work) fw_iso_context_flush_completions(irq_target->context); }