From: Shiju Jose <shiju.jose@huawei.com>

Date: Thu, 2 Feb 2023 18:23:09 +0000

Subject: tracing: Fix poll() and select() do not work on per_cpu trace_pipe

 and trace_pipe_raw

Git-commit: 3e46d910d8acf94e5360126593b68bf4fee4c4a1

Patch-mainline: v6.2-rc8

References: git-fixes, bsc#1209841

poll() and select() on per_cpu trace_pipe and trace_pipe_raw do not work

since kernel 6.1-rc6. This issue is seen after the commit

42fb0a1e84ff525ebe560e2baf9451ab69127e2b ("tracing/ring-buffer: Have

polling block on watermark").

This issue is firstly detected and reported, when testing the CXL error

events in the rasdaemon and also erified using the test application for poll()

and select().

This issue occurs for the per_cpu case, when calling the ring_buffer_poll_wait(),

in kernel/trace/ring_buffer.c, with the buffer_percent > 0 and then wait until the

percentage of pages are available. The default value set for the buffer_percent is 50

in the kernel/trace/trace.c.

As a fix, allow userspace application could set buffer_percent as 0 through

the buffer_percent_fops, so that the task will wake up as soon as data is added

to any of the specific cpu buffer.

Link: https://lore.kernel.org/linux-trace-kernel/20230202182309.742-2-shiju.jose@huawei.com

Cc: <mhiramat@kernel.org>

Cc: <mchehab@kernel.org>

Cc: <linux-edac@vger.kernel.org>

Cc: stable@vger.kernel.org

Fixes: 42fb0a1e84ff5 ("tracing/ring-buffer: Have polling block on watermark")

Signed-off-by: Shiju Jose <shiju.jose@huawei.com>

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Acked-by: Petr Pavlu <petr.pavlu@suse.com>

---

 kernel/trace/trace.c | 3 ---

 1 file changed, 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c

index 78ed5f1baa8c..c9e40f692650 100644

--- a/kernel/trace/trace.c

+++ b/kernel/trace/trace.c

@@ -9148,9 +9148,6 @@ buffer_percent_write(struct file *filp, const char __user *ubuf,

 	if (val > 100)

 		return -EINVAL;

-	if (!val)

-		val = 1;

-

 	tr->buffer_percent = val;

 	(*ppos)++;