From: Vincent Donnefort vdonnefort@google.com

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-vdonnefo...

Cc: stable@vger.kernel.org Fixes: 6721cb6002262 ("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 --- kernel/trace/ring_buffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 13aaf5e85b81..fd4bfe3ecf01 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -944,7 +944,7 @@ __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu, full = 0; } else { if (!cpumask_test_cpu(cpu, buffer->cpumask)) - return -EINVAL; + return EPOLLERR;

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