linux-kernel - [PATCH] ring-buffer: Clean ring_buffer_poll

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Message-ID: <20240131140955.3322792-1-vdonnefort@google.com>
Date: Wed, 31 Jan 2024 14:09:55 +0000
From: Vincent Donnefort <vdonnefort@...gle.com>
To: rostedt@...dmis.org, mhiramat@...nel.org, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org
Cc: mathieu.desnoyers@...icios.com, kernel-team@...roid.com, 
	Vincent Donnefort <vdonnefort@...gle.com>
Subject: [PATCH] ring-buffer: Clean ring_buffer_poll_wait() error return

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.

Signed-off-by: Vincent Donnefort <vdonnefort@...gle.com>

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;

base-commit: 29142dc92c37d3259a33aef15b03e6ee25b0d188
-- 
2.43.0.429.g432eaa2c6b-goog