Re: [PATCH v4 0/2] ALSA: firewire-lib: restore process context workqueue to prevent deadlock

[Takashi Sakamoto <o-takashi@sakamocchi.jp>]

Hi,

On Tue, Jul 30, 2024 at 07:53:23PM +0000, Edmund Raile wrote:
> This patchset serves to prevent an AB/BA deadlock:
> 
> 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
> 
> 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.
> 
> Cc: stable@vger.kernel.org
> 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):
>   Revert "ALSA: firewire-lib: obsolete workqueue for period update"
>   Revert "ALSA: firewire-lib: operate for period elapse event in process
>     context"
> 
>  sound/firewire/amdtp-stream.c | 38 ++++++++++++++++++++++-------------
>  sound/firewire/amdtp-stream.h |  1 +
>  2 files changed, 25 insertions(+), 14 deletions(-)

They look good to me.

Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

I appreciate your long effort to solve the issue.


Thanks

Takashi Sakamoto