// 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.
+ //
+ // Use another work item for period elapsed event to prevent the following AB/BA
+ // deadlock:
+ //
+ // thread 1 thread 2
+ // ================================= =================================
+ // A.work item (process) pcm ioctl (process)
+ // v v
+ // process_rx_packets() B.PCM stream lock
+ // process_tx_packets() v
+ // v callbacks in snd_pcm_ops
+ // update_pcm_pointers() v
+ // snd_pcm_elapsed() fw_iso_context_flush_completions()
+ // snd_pcm_stream_lock_irqsave() disable_work_sync()
+ // v v
+ // wait until release of B wait until A exits
if (!pcm->runtime->no_period_wakeup)
queue_work(system_highpri_wq, &s->period_work);
}
static inline void cancel_stream(struct amdtp_stream *s)
{
+ struct work_struct *work = current_work();
+
s->packet_index = -1;
- if (in_softirq())
+
+ // Detect work items for any isochronous context. The work item for pcm_period_work()
+ // should be avoided since the call of snd_pcm_period_elapsed() can reach via
+ // snd_pcm_ops.pointer() under acquiring PCM stream(group) lock and causes dead lock at
+ // snd_pcm_stop_xrun().
+ if (work && work != &s->period_work)
amdtp_stream_pcm_abort(s);
WRITE_ONCE(s->pcm_buffer_pointer, SNDRV_PCM_POS_XRUN);
}
struct amdtp_stream *irq_target = d->irq_target;
if (irq_target && amdtp_stream_running(irq_target)) {
- // 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()
+ // The work item to call snd_pcm_period_elapsed() can reach here by the call of
+ // snd_pcm_ops.pointer(), however less packets would be available then. Therefore
+ // the following call is just for user process contexts.
if (current_work() != &s->period_work)
fw_iso_context_flush_completions(irq_target->context);
}
projects / thirdparty / kernel / linux.git / commitdiff
