Commit ce47b798 authored by Vincent Donnefort's avatar Vincent Donnefort Committed by Marc Zyngier
Browse files

tracing: Non-consuming read for trace remotes with an offline CPU 



When a trace_buffer is created while a CPU is offline, this CPU is
cleared from the trace_buffer CPU mask, preventing the creation of a
non-consuming iterator (ring_buffer_iter). For trace remotes, it means
the iterator fails to be allocated (-ENOMEM) even though there are
available ring buffers in the trace_buffer.

For non-consuming reads of trace remotes, skip missing ring_buffer_iter
to allow reading the available ring buffers.

Acked-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: default avatarVincent Donnefort <vdonnefort@google.com>
Link: https://patch.msgid.link/20260401045100.3394299-2-vdonnefort@google.com


Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
parent 58b4bd18

kernel/trace/trace_remote.c

+19 −3
Original line number Diff line number Diff line
@@ -282,6 +282,14 @@ static void trace_remote_put(struct trace_remote *remote) 
	trace_remote_try_unload(remote);

}



static bool trace_remote_has_cpu(struct trace_remote *remote, int cpu)

{

	if (cpu == RING_BUFFER_ALL_CPUS)

		return true;



	return ring_buffer_poll_remote(remote->trace_buffer, cpu) == 0;

}



static void __poll_remote(struct work_struct *work)

{

	struct delayed_work *dwork = to_delayed_work(work);
@@ -324,6 +332,10 @@ static int __alloc_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu) 
		iter->rb_iters[cpu] = ring_buffer_read_start(iter->remote->trace_buffer, cpu,

							     GFP_KERNEL);

		if (!iter->rb_iters[cpu]) {

			/* This CPU isn't part of trace_buffer. Skip it */

			if (!trace_remote_has_cpu(iter->remote, cpu))

				continue;



			__free_ring_buffer_iter(iter, RING_BUFFER_ALL_CPUS);

			return -ENOMEM;

		}
@@ -347,10 +359,10 @@ static struct trace_remote_iterator 
	if (ret)

		return ERR_PTR(ret);



	/* Test the CPU */

	ret = ring_buffer_poll_remote(remote->trace_buffer, cpu);

	if (ret)

	if (!trace_remote_has_cpu(remote, cpu)) {

		ret = -ENODEV;

		goto err;

	}



	iter = kzalloc_obj(*iter);

	if (iter) {
@@ -361,6 +373,7 @@ static struct trace_remote_iterator 


		switch (type) {

		case TRI_CONSUMING:

			ring_buffer_poll_remote(remote->trace_buffer, cpu);

			INIT_DELAYED_WORK(&iter->poll_work, __poll_remote);

			schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(remote->poll_ms));

			break;
@@ -476,6 +489,9 @@ __peek_event(struct trace_remote_iterator *iter, int cpu, u64 *ts, unsigned long 
		return ring_buffer_peek(iter->remote->trace_buffer, cpu, ts, lost_events);

	case TRI_NONCONSUMING:

		rb_iter = __get_rb_iter(iter, cpu);

		if (!rb_iter)

			return NULL;



		rb_evt = ring_buffer_iter_peek(rb_iter, ts);

		if (!rb_evt)

			return NULL;