[PATCH] perf auxtrace: Fix auxtrace queue conflict

[PATCH] perf auxtrace: Fix auxtrace queue conflict

[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.

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 <ak@linux.intel.com>
Fixes: e502789302a6 ("perf auxtrace: Add helpers for queuing AUX area tracing data")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 tools/perf/util/auxtrace.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
index 953f4afacd3b..5b6ccb90b397 100644
--- a/tools/perf/util/auxtrace.c
+++ b/tools/perf/util/auxtrace.c
@@ -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++;
-- 
2.17.1

Re: [PATCH] perf auxtrace: Fix auxtrace queue conflict

[Andi Kleen]

On Mon, Mar 08, 2021 at 05:11:43PM +0200, Adrian Hunter wrote:
> 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.

Thanks!

Reviewed-by: Andi Kleen <ak@linux.intel.com>

-Andi

Re: [PATCH] perf auxtrace: Fix auxtrace queue conflict

[Arnaldo Carvalho de Melo]

Em Mon, Mar 08, 2021 at 08:54:37AM -0800, Andi Kleen escreveu:
> On Mon, Mar 08, 2021 at 05:11:43PM +0200, Adrian Hunter wrote:
> > 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.
> 
> Thanks!
> 
> Reviewed-by: Andi Kleen <ak@linux.intel.com>

Thanks, applied.

- Arnaldo