[PATCH v3 3/3] ALSA: firewire-lib: amdtp-stream work queue inline description

Edmund Raile
2024-07-29T21:42:31Z

Replace prior inline description to prevent future deadlock.

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/kwryofzdmjvzkuw6j3clftsxmoolynljztxqwg76hzeo4simnl@jn3eo7pe642q/
Signed-off-by: Edmund Raile <edmund.raile@protonmail.com>
---
sound/firewire/amdtp-stream.c | 20 ++++++--------------
1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c
index a07b0452267d..7438999e0510 100644
--- a/sound/firewire/amdtp-stream.c
+++ b/sound/firewire/amdtp-stream.c
@@ -1857,20 +1857,12 @@ unsigned long amdtp_domain_stream_pcm_pointer(struct amdtp_domain *d,
struct amdtp_stream *irq_target = d->irq_target;

if (irq_target && amdtp_stream_running(irq_target)) {
- // 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
+ // use wq to prevent AB/BA deadlock competition for
+ // substream lock:
+ // fw_iso_context_flush_completions() acquires
+ // lock by ohci_flush_iso_completions(),
+ // amdtp-stream process_rx_packets() attempts to
+ // acquire same lock by snd_pcm_elapsed()
if (current_work() != &s->period_work)
fw_iso_context_flush_completions(irq_target->context);
}
--
2.45.2