From: Shiju Jose shiju.jose@huawei.com
commit 3e46d910d8acf94e5360126593b68bf4fee4c4a1 upstream.
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@h...
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/trace/trace.c | 3 --- 1 file changed, 3 deletions(-)
--- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8569,9 +8569,6 @@ buffer_percent_write(struct file *filp, if (val > 100) return -EINVAL;
- if (!val) - val = 1; - tr->buffer_percent = val;
(*ppos)++;