The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
Possible dependencies:
01b2a5217173 ("tracing: Add ioctl() to force ring buffer waiters to wake up")
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 01b2a52171735c6eea80ee2f355f32bea6c41418 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
Date: Thu, 29 Sep 2022 09:50:29 -0400
Subject: [PATCH] tracing: Add ioctl() to force ring buffer waiters to wake up
If a process is waiting on the ring buffer for data, there currently isn't
a clean way to force it to wake up. Add an ioctl call that will force any
tasks that are waiting on the trace_pipe_raw file to wake up.
Link: https://lkml.kernel.org/r/20220929095029.117f913f@xxxxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Fixes: e30f53aad2202 ("tracing: Do not busy wait in buffer splice")
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e101b0764b39..58afc83afc9d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8349,12 +8349,34 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
return ret;
}
+/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */
+static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+ struct ftrace_buffer_info *info = file->private_data;
+ struct trace_iterator *iter = &info->iter;
+
+ if (cmd)
+ return -ENOIOCTLCMD;
+
+ mutex_lock(&trace_types_lock);
+
+ iter->wait_index++;
+ /* Make sure the waiters see the new wait_index */
+ smp_wmb();
+
+ ring_buffer_wake_waiters(iter->array_buffer->buffer, iter->cpu_file);
+
+ mutex_unlock(&trace_types_lock);
+ return 0;
+}
+
static const struct file_operations tracing_buffers_fops = {
.open = tracing_buffers_open,
.read = tracing_buffers_read,
.poll = tracing_buffers_poll,
.release = tracing_buffers_release,
.splice_read = tracing_buffers_splice_read,
+ .unlocked_ioctl = tracing_buffers_ioctl,
.llseek = no_llseek,
};
