Commit 8eed2abb authored Jan 31, 2024 by Vincent Donnefort Committed by Greg Kroah-Hartman Feb 23, 2024

ring-buffer: Clean ring_buffer_poll_wait() error return

commit 66bbea9ed6446b8471d365a22734dc00556c4785 upstream.

The return type for ring_buffer_poll_wait() is __poll_t. This is behind
the scenes an unsigned where we can set event bits. In case of a
non-allocated CPU, we do return instead -EINVAL (0xffffffea). Lucky us,
this ends up setting few error bits (EPOLLERR | EPOLLHUP | EPOLLNVAL), so
user-space at least is aware something went wrong.

Nonetheless, this is an incorrect code. Replace that -EINVAL with a
proper EPOLLERR to clean that output. As this doesn't change the
behaviour, there's no need to treat this change as a bug fix.

Link: https://lore.kernel.org/linux-trace-kernel/20240131140955.3322792-1-vdonnefort@google.com

Cc: stable@vger.kernel.org
Fixes: 6721cb60 ("ring-buffer: Do not poll non allocated cpu buffers")
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 4a0efde7

kernel/trace/ring_buffer.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -676,7 +676,7 @@ __poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
		work = &buffer->irq_work;
		else {
		if (!cpumask_test_cpu(cpu, buffer->cpumask))
		return -EINVAL;
		return EPOLLERR;

		cpu_buffer = buffer->buffers[cpu];
		work = &cpu_buffer->irq_work;