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: 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 041b91c2ba10a3bc70d24a4e49692d62639b5019..4a43b8846b49f83eaf4cf1bf1c27cda560358a69 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1008,7 +1008,7 @@ __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;