[Devel] [PATCH RHEL9 COMMIT] ms/tracing/osnoise: Properly unhook events if start_per_cpu_kthreads() fails

[Konstantin Khorenko]

The commit is pushed to "branch-rh9-5.14.vz9.1.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh9-5.14.0-4.vz9.10.38
------>
commit 1113d0cca4df479b9b19ac34428b1831900953a3
Author: Nikita Yushchenko <nikita.yushchenko at virtuozzo.com>
Date:   Tue Jan 11 13:39:16 2022 +0300

    ms/tracing/osnoise: Properly unhook events if start_per_cpu_kthreads() fails
    
    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.
    
    msFixes: bce29ac9ce0b ("trace: Add osnoise tracer")
    https://jira.sw.ru/browse/PSBM-136911
    Signed-off-by: Nikita Yushchenko <nikita.yushchenko at virtuozzo.com>
    
    The patch is not is ms yet: https://lkml.org/lkml/2022/1/9/108
---
 kernel/trace/trace_osnoise.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 43acd168c06f..e380c02847b3 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1932,6 +1932,13 @@ static int osnoise_hook_events(void)
 	return -EINVAL;
 }
 
+static void osnoise_unhook_events(void)
+{
+	unhook_thread_events();
+	unhook_softirq_events();
+	unhook_irq_events();
+}
+
 static int __osnoise_tracer_start(struct trace_array *tr)
 {
 	int retval;
@@ -1949,7 +1956,14 @@ static int __osnoise_tracer_start(struct trace_array *tr)
 
 	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 trace_array *tr)
 
 	stop_per_cpu_kthreads();
 
-	unhook_irq_events();
-	unhook_softirq_events();
-	unhook_thread_events();
+	osnoise_unhook_events();
 
 	osnoise_busy = false;
 }