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perf auxtrace: Fix auxtrace queue conflict

PATCH Applied Adrian Hunter 3 participants 3 messages Mar 8, 2021 – Mar 9, 2021 perf events

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Adrian Hunter

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PATCH 1/1 perf auxtrace: Fix auxtrace queue conflict

The only requirement of an auxtrace queue is that the buffers are in time order. That is achieved by making separate queues for separate perf buffer or AUX area buffer mmaps.

That generally means a separate queue per cpu for per-cpu contexts, and a separate queue per thread for per-task contexts.

When buffers are added to a queue, perf checks that the buffer cpu and thread id (tid) match the queue cpu and thread id.

However, generally, that need not be true, and perf will queue buffers correctly anyway, so the check is not needed.

In addition, the check gets erroneously hit when using sample mode to trace multiple threads.

Consequently, fix that case by removing the check.

Reported-by Andi Kleen <[email protected]>
Fixes e502789302a6 ("perf auxtrace: Add helpers for queuing AUX area tracing data")
Signed-off-by Adrian Hunter <[email protected]>
---
 tools/perf/util/auxtrace.c | 4 ----
 1 file changed, 4 deletions(-)
tools/perf/util/auxtrace.c +0 -4
index 953f4afacd3b..5b6ccb90b397 100644
@@ -298,10 +298,6 @@ static int auxtrace_queues__queue_buffer(struct auxtrace_queues *queues,
 		queue->set = true;
 		queue->tid = buffer->tid;
 		queue->cpu = buffer->cpu;
-	} else if (buffer->cpu != queue->cpu || buffer->tid != queue->tid) {
-		pr_err("auxtrace queue conflict: cpu %d, tid %d vs cpu %d, tid %d\n",
-		       queue->cpu, queue->tid, buffer->cpu, buffer->tid);
-		return -EINVAL;
 	}
 
 	buffer->buffer_nr = queues->next_buffer_nr++;
Signature · 1 line
2.17.1
Reviewed-by on v1 1/1
#1 lore raw
Quoted 10 lines · Adrian Hunter

The only requirement of an auxtrace queue is that the buffers are in time order. That is achieved by making separate queues for separate perf buffer or AUX area buffer mmaps.

That generally means a separate queue per cpu for per-cpu contexts, and a separate queue per thread for per-task contexts.

When buffers are added to a queue, perf checks that the buffer cpu and thread id (tid) match the queue cpu and thread id.

Quoted 7 lines

However, generally, that need not be true, and perf will queue buffers correctly anyway, so the check is not needed.

In addition, the check gets erroneously hit when using sample mode to trace multiple threads.

Consequently, fix that case by removing the check.

Thanks!

Reviewed-by Andi Kleen <[email protected]>

-Andi

maintainer Applied
#2 lore raw

Em Mon, Mar 08, 2021 at 08:54:37AM -0800, Andi Kleen escreveu:

Quoted 14 lines · Adrian Hunter
Quoted 13 lines

The only requirement of an auxtrace queue is that the buffers are in time order. That is achieved by making separate queues for separate perf buffer or AUX area buffer mmaps.

That generally means a separate queue per cpu for per-cpu contexts, and a separate queue per thread for per-task contexts.

When buffers are added to a queue, perf checks that the buffer cpu and thread id (tid) match the queue cpu and thread id.

However, generally, that need not be true, and perf will queue buffers correctly anyway, so the check is not needed.

Quoted 8 lines
Quoted 4 lines

In addition, the check gets erroneously hit when using sample mode to trace multiple threads.

Consequently, fix that case by removing the check.

Thanks!

Reviewed-by Andi Kleen <[email protected]>

Thanks, applied.

- Arnaldo