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Message-ID: <bd4d3e70-400d-9c82-7b73-a2d695e86b58@virtuozzo.com>
Date: Wed, 18 Nov 2020 15:05:20 +0300
From: Vasily Averin <vvs@...tuozzo.com>
To: Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] tracing: remove WARN_ON in start_thread()
This patch reverts commit 978defee11a5 ("tracing: Do a WARN_ON()
if start_thread() in hwlat is called when thread exists")
.start hook can be legally called several times if according
tracer is stopped
screen window 1
[root@...alhost ~]# echo 1 > /sys/kernel/tracing/events/kmem/kfree/enable
[root@...alhost ~]# echo 1 > /sys/kernel/tracing/options/pause-on-trace
[root@...alhost ~]# less -F /sys/kernel/tracing/trace
screen window 2
[root@...alhost ~]# cat /sys/kernel/debug/tracing/tracing_on
0
[root@...alhost ~]# echo hwlat > /sys/kernel/debug/tracing/current_tracer
[root@...alhost ~]# echo 1 > /sys/kernel/debug/tracing/tracing_on
[root@...alhost ~]# cat /sys/kernel/debug/tracing/tracing_on
0
[root@...alhost ~]# echo 2 > /sys/kernel/debug/tracing/tracing_on
triggers warning in dmesg:
WARNING: CPU: 3 PID: 1403 at kernel/trace/trace_hwlat.c:371 hwlat_tracer_start+0xc9/0xd0
Fixes: 978defee11a5 ("tracing: Do a WARN_ON() if start_thread() in hwlat is called when thread exists")
Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
---
kernel/trace/trace_hwlat.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index c9ad5c6..d071fc2 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -368,7 +368,7 @@ static int start_kthread(struct trace_array *tr)
struct task_struct *kthread;
int next_cpu;
- if (WARN_ON(hwlat_kthread))
+ if (hwlat_kthread)
return 0;
/* Just pick the first CPU on first iteration */
--
1.8.3.1
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