This is a note to let you know that I've just added the patch titled
tracing: Fix warning in trace_buffered_event_disable()
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tracing-fix-warning-in-trace_buffered_event_disable.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit bb4da883bf091f2de493dc0f88b5dde230038ea3
Author: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
Date: Wed Jul 26 17:58:04 2023 +0800
tracing: Fix warning in trace_buffered_event_disable()
[ Upstream commit dea499781a1150d285c62b26659f62fb00824fce ]
Warning happened in trace_buffered_event_disable() at
WARN_ON_ONCE(!trace_buffered_event_ref)
Call Trace:
? __warn+0xa5/0x1b0
? trace_buffered_event_disable+0x189/0x1b0
__ftrace_event_enable_disable+0x19e/0x3e0
free_probe_data+0x3b/0xa0
unregister_ftrace_function_probe_func+0x6b8/0x800
event_enable_func+0x2f0/0x3d0
ftrace_process_regex.isra.0+0x12d/0x1b0
ftrace_filter_write+0xe6/0x140
vfs_write+0x1c9/0x6f0
[...]
The cause of the warning is in __ftrace_event_enable_disable(),
trace_buffered_event_enable() was called once while
trace_buffered_event_disable() was called twice.
Reproduction script show as below, for analysis, see the comments:
```
#!/bin/bash
cd /sys/kernel/tracing/
# 1. Register a 'disable_event' command, then:
# 1) SOFT_DISABLED_BIT was set;
# 2) trace_buffered_event_enable() was called first time;
echo 'cmdline_proc_show:disable_event:initcall:initcall_finish' > \
set_ftrace_filter
# 2. Enable the event registered, then:
# 1) SOFT_DISABLED_BIT was cleared;
# 2) trace_buffered_event_disable() was called first time;
echo 1 > events/initcall/initcall_finish/enable
# 3. Try to call into cmdline_proc_show(), then SOFT_DISABLED_BIT was
# set again!!!
cat /proc/cmdline
# 4. Unregister the 'disable_event' command, then:
# 1) SOFT_DISABLED_BIT was cleared again;
# 2) trace_buffered_event_disable() was called second time!!!
echo '!cmdline_proc_show:disable_event:initcall:initcall_finish' > \
set_ftrace_filter
```
To fix it, IIUC, we can change to call trace_buffered_event_enable() at
fist time soft-mode enabled, and call trace_buffered_event_disable() at
last time soft-mode disabled.
Link: https://lore.kernel.org/linux-trace-kernel/20230726095804.920457-1-zhengyejian1@xxxxxxxxxx
Cc: <mhiramat@xxxxxxxxxx>
Fixes: 0fc1b09ff1ff ("tracing: Use temp buffer when filtering events")
Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index f8ed66f38175b..a46d34d840f69 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -371,7 +371,6 @@ static int __ftrace_event_enable_disable(struct trace_event_file *file,
{
struct trace_event_call *call = file->event_call;
struct trace_array *tr = file->tr;
- unsigned long file_flags = file->flags;
int ret = 0;
int disable;
@@ -395,6 +394,8 @@ static int __ftrace_event_enable_disable(struct trace_event_file *file,
break;
disable = file->flags & EVENT_FILE_FL_SOFT_DISABLED;
clear_bit(EVENT_FILE_FL_SOFT_MODE_BIT, &file->flags);
+ /* Disable use of trace_buffered_event */
+ trace_buffered_event_disable();
} else
disable = !(file->flags & EVENT_FILE_FL_SOFT_MODE);
@@ -433,6 +434,8 @@ static int __ftrace_event_enable_disable(struct trace_event_file *file,
if (atomic_inc_return(&file->sm_ref) > 1)
break;
set_bit(EVENT_FILE_FL_SOFT_MODE_BIT, &file->flags);
+ /* Enable use of trace_buffered_event */
+ trace_buffered_event_enable();
}
if (!(file->flags & EVENT_FILE_FL_ENABLED)) {
@@ -472,15 +475,6 @@ static int __ftrace_event_enable_disable(struct trace_event_file *file,
break;
}
- /* Enable or disable use of trace_buffered_event */
- if ((file_flags & EVENT_FILE_FL_SOFT_DISABLED) !=
- (file->flags & EVENT_FILE_FL_SOFT_DISABLED)) {
- if (file->flags & EVENT_FILE_FL_SOFT_DISABLED)
- trace_buffered_event_enable();
- else
- trace_buffered_event_disable();
- }
-
return ret;
}
