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FAILED: patch "[PATCH] tracing: Add ioctl() to force ring buffer waiters to wake up" failed to apply to 4.9-stable tree

PATCH [email protected] 1 participant 1 message Oct 16, 2022

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The patch below does not apply to the 4.9-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 <[email protected]>.

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)" <[email protected]>
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/[email protected] open here
Cc [email protected]
Cc Ingo Molnar <[email protected]>
Cc Andrew Morton <[email protected]>
Fixes e30f53aad2202 ("tracing: Do not busy wait in buffer splice")
Signed-off-by Steven Rostedt (Google) <[email protected]>
kernel/trace/trace.c +22 -0
index e101b0764b39..58afc83afc9d 100644
@@ -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,
 };