[PATCH] tracing/eprobe: Install the trigger for every instance that enables the eprobe

[PATCH] tracing/eprobe: Install the trigger for every instance that enables the eprobe

[David Carlier]

The eprobe trigger lives in the instance of the enabling file, but it is
only added when the eprobe is first enabled and only removed when the
last file goes away. A second instance then records nothing, and the
first instance's trigger is left behind once the eprobe is disabled
there, so the eprobe can be deleted while that trigger still uses it.

Add and remove the trigger for each file.

Fixes: 7491e2c44278 ("tracing: Add a probe that attaches to trace events")
Cc: stable@vger.kernel.org
Signed-off-by: David Carlier <devnexen@gmail.com>
---
 kernel/trace/trace_eprobe.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
index 998e6390937a..a0bc6fa1fc69 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -661,20 +661,20 @@ static int enable_trace_eprobe(struct trace_event_call *call,
 	} else
 		trace_probe_set_flag(tp, TP_FLAG_PROFILE);
 
-	if (enabled)
+	/* The trigger lives in the instance of the file, add it for each file */
+	if (!file && enabled)
 		return 0;
 
 	for_each_trace_eprobe_tp(ep, tp) {
 		ret = enable_eprobe(ep, file);
 		if (ret)
 			break;
-		enabled = true;
 		cnt++;
 	}
 
 	if (ret) {
 		/* Failed to enable one of them. Roll back all */
-		if (enabled) {
+		if (cnt) {
 			/*
 			 * It's a bug if one failed for something other than memory
 			 * not being available but another eprobe succeeded.
@@ -709,18 +709,11 @@ static int disable_trace_eprobe(struct trace_event_call *call,
 	if (file) {
 		if (!trace_probe_get_file_link(tp, file))
 			return -ENOENT;
-		if (!trace_probe_has_single_file(tp))
-			goto out;
-		trace_probe_clear_flag(tp, TP_FLAG_TRACE);
-	} else
-		trace_probe_clear_flag(tp, TP_FLAG_PROFILE);
-
-	if (!trace_probe_is_enabled(tp)) {
 		for_each_trace_eprobe_tp(ep, tp)
 			disable_eprobe(ep, file->tr);
-	}
+	} else
+		trace_probe_clear_flag(tp, TP_FLAG_PROFILE);
 
- out:
 	if (file)
 		/*
 		 * Synchronization is done in below function. For perf event,
-- 
2.55.0

Re: [PATCH] tracing/eprobe: Install the trigger for every instance that enables the eprobe

[Masami Hiramatsu (Google)]

On Sat, 31 Oct 2026 20:39:15 +0000, David Carlier <devnexen@gmail.com> wrote:

> diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
> --- a/kernel/trace/trace_eprobe.c
> +++ b/kernel/trace/trace_eprobe.c
> @@ -661,20 +661,20 @@ static int enable_trace_eprobe(struct trace_event_call *call,
>  		trace_probe_set_flag(tp, TP_FLAG_PROFILE);
>  
> +	/* The trigger lives in the instance of the file, add it for each file */
> +	if (!file && enabled)

Hmm, when reviewing this patch, I found file should not be NULL
because enable/disable_trace_eprobe() are only ever called via
eprobe_register() with `TRACE_REG_REGISTER/UNREGISTER` where `file` is
always non-NULL.

So we should expect !file case is a bug. So at the entry of these functions
we can add:

	if (WARN_ON_ONCE(!file))
		return -EINVAL;

and remove !file blocks.

Thanks!

>  		return 0;
>  
>  	for_each_trace_eprobe_tp(ep, tp) {

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>