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tracing: Fix warning in trace_buffered_event_disable()

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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@huawei.com

Cc: <mhiramat@kernel.org>
Fixes: 0fc1b09ff1 ("tracing: Use temp buffer when filtering events")
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Zheng Yejian 2023-07-26 17:58:04 +08:00 committed by Steven Rostedt (Google)
parent 800959e697
commit dea499781a
1 changed files with 4 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
kernel/trace/trace_events.c
View File

@ -611,7 +611,6 @@ 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;
@ -635,6 +634,8 @@ 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);
@ -673,6 +674,8 @@ 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)) {
@ -712,15 +715,6 @@ 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;
}