From: Nikita Yushchenko <nikita.yushchenko@virtuozzo.com>
Date: Sun, 9 Jan 2022 18:34:59 +0300
Subject: tracing/osnoise: Properly unhook events if start_per_cpu_kthreads()
 fails
Git-commit: 0878355b51f5f26632e652c848a8e174bb02d22d
Patch-mainline: v5.16 or v5.16-rc9 (next release)
References: git-fixes

If start_per_cpu_kthreads() called from osnoise_workload_start() returns
error, event hooks are left in broken state: unhook_irq_events() called
but unhook_thread_events() and unhook_softirq_events() not called, and
trace_osnoise_callback_enabled flag not cleared.

On the next tracer enable, hooks get not installed due to
trace_osnoise_callback_enabled flag.

And on the further tracer disable an attempt to remove non-installed
hooks happened, hitting a WARN_ON_ONCE() in tracepoint_remove_func().

Fix the error path by adding the missing part of cleanup.
While at this, introduce osnoise_unhook_events() to avoid code
duplication between this error path and normal tracer disable.

Link: https://lkml.kernel.org/r/20220109153459.3701773-1-nikita.yushchenko@virtuozzo.com

Cc: stable@vger.kernel.org
Fixes: bce29ac9ce0b ("trace: Add osnoise tracer")
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Nikita Yushchenko <nikita.yushchenko@virtuozzo.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 kernel/trace/trace_osnoise.c |   20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1835,6 +1835,13 @@ static const struct file_operations cpus
 	.llseek		= generic_file_llseek,
 };
 
+static void osnoise_unhook_events(void)
+{
+	unhook_thread_events();
+	unhook_softirq_events();
+	unhook_irq_events();
+}
+
 /*
  * init_tracefs - A function to initialize the tracefs interface files
  *
@@ -1949,7 +1956,14 @@ static int __osnoise_tracer_start(struct
 
 	retval = start_per_cpu_kthreads(tr);
 	if (retval) {
-		unhook_irq_events();
+		trace_osnoise_callback_enabled = false;
+		/*
+		 * Make sure that ftrace_nmi_enter/exit() see
+		 * trace_osnoise_callback_enabled as false before continuing.
+		 */
+		barrier();
+
+		osnoise_unhook_events();
 		return retval;
 	}
 
@@ -1981,9 +1995,7 @@ static void osnoise_tracer_stop(struct t
 
 	stop_per_cpu_kthreads();
 
-	unhook_irq_events();
-	unhook_softirq_events();
-	unhook_thread_events();
+	osnoise_unhook_events();
 
 	osnoise_busy = false;
 }