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fix the deadlock issue when mailbox trace is configured. #4700

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keyonjie wants to merge 2 commits into from
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fix the deadlock issue when mailbox trace is configured. #4700

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eca9f70
dma-trace: hold the lock during switching on/off the trace
keyonjie Aug 31, 2021
d639e5e
trace: don't hold trace->lock during dma_trace_on/off
keyonjie Aug 31, 2021
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22 changes: 19 additions & 3 deletions src/trace/dma-trace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -475,26 +475,42 @@ void dma_trace_flush(void *t)
void dma_trace_on(void)
{
struct dma_trace_data *trace_data = dma_trace_data_get();
uint32_t flags;

if (!trace_data || trace_data->enabled)
if (!trace_data)
return;

trace_data->enabled = 1;
spin_lock_irq(&trace_data->lock, flags);
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@lyakh lyakh Sep 1, 2021

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do we have a good understanding of what this lock is protecting, vs. what the other trace lock is protecting? The use of this lock doesn't seem to be fully consistent. E.g. dtrace_event() this lock is also covering the test of .copy_in_progress, but not in a consistent way, because both locations where .copy_in_progress is set to 1 aren't protected by that lock, so, holding the lock while testing it doesn't help. Why do we have to lock here at all?


if (trace_data->enabled)
goto finish;

schedule_task(&trace_data->dmat_work, DMA_TRACE_PERIOD,
DMA_TRACE_PERIOD);
trace_data->enabled = 1;
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@plbossart plbossart Aug 31, 2021

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you're setting this flag protected by the spinlock, but you test it on like 480 without any protection.
Is this intentional?


finish:
spin_unlock_irq(&trace_data->lock, flags);
}

void dma_trace_off(void)
{
struct dma_trace_data *trace_data = dma_trace_data_get();
uint32_t flags;

if (!trace_data || !trace_data->enabled)
if (!trace_data)
return;

spin_lock_irq(&trace_data->lock, flags);

if (!trace_data->enabled)
goto finish;

schedule_task_cancel(&trace_data->dmat_work);
trace_data->enabled = 0;

finish:
spin_unlock_irq(&trace_data->lock, flags);
}

static int dtrace_calc_buf_overflow(struct dma_trace_buf *buffer,
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20 changes: 14 additions & 6 deletions src/trace/trace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -486,11 +486,15 @@ void trace_on(void)
struct trace *trace = trace_get();
uint32_t flags;

spin_lock_irq(&trace->lock, flags);

trace->enable = 1;
/*
* To avoid dead lock, we should not do this with trace->lock held,
* as there is log tracing inside the dma_trace_on(), which will ask
* for holding trace->lock also.
*/
dma_trace_on();

spin_lock_irq(&trace->lock, flags);
trace->enable = 1;
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@plbossart plbossart Aug 31, 2021

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so the trace is enabled after the 'dma trace'. that seems surprising?

spin_unlock_irq(&trace->lock, flags);
}

Expand All @@ -499,11 +503,15 @@ void trace_off(void)
struct trace *trace = trace_get();
uint32_t flags;

spin_lock_irq(&trace->lock, flags);

trace->enable = 0;
/*
* To avoid dead lock, we should not do this with trace->lock held,
* as there is log tracing inside the dma_trace_off(), which will ask
* for holding trace->lock also.
*/
dma_trace_off();

spin_lock_irq(&trace->lock, flags);
trace->enable = 0;
spin_unlock_irq(&trace->lock, flags);
}

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