Re: [PATCH v11 08/11] tracing: wprobe: Add wprobe event trigger

On Sun,  2 Aug 2026 17:19:55 +0900
"Masami Hiramatsu (Google)" [off-list ref] wrote:

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

Add wprobe event trigger to set and clear the watch event dynamically.
This allows us to set an watchpoint on a given local variables and
a slab object instead of static objects.

The trigger syntax is below:

  - set_wprobe:WPROBE:FIELD[+OFFSET][:COUNT] [if FILTER]
  - clear_wprobe:WPROBE[:FIELD[+OFFSET]][:COUNT] [if FILTER]

set_wprobe sets the address pointed by FIELD[+offset] to the WPROBE
event. The FIELD is the field name of trigger event.
clear_wprobe clears the watch address of WPROBE event. If the FIELD
option is specified, it clears only if the current watch address is
same as the given FIELD[+OFFSET] value.
COUNT is the max number of activating trigger.

The set_wprobe trigger does not change the type and length, these
must be set when creating a new wprobe.

Also, the WPROBE event must be disabled when setting the new trigger
and it will be busy afterwards. Recommended usage is to add a new
wprobe at NULL address and keep disabled.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v11:
  - Use new modify_local_hw_breakpoint_addr() API.
  - Add tracepoint_synchronize_unregister() in wprobe_unregister_trigger()
    and parse error path.
  - Safely check tw->bp_event for NULL in trace_wprobe_update_local() to
    prevent race conditions.
  - Use event_trigger_data::private_data_free.
  - Add count option support.

Oops, I made a mistake on this count support.

+static int wprobe_trigger_cmd_parse(struct event_command *cmd_ops,
+				    struct trace_event_file *file,
+				    char *glob, char *cmd,
+				    char *param_and_filter)
+{

[...]

+	/* count is optional, "unlimited" by default */
+	count_str = strsep(&param, ":");
+	if (count_str) {
+		long val;
+
+		if (strcmp(count_str, "unlimited")) {
+			if (str_has_prefix(count_str, "count="))
+				count_str += 6;
+			if (kstrtol(count_str, 0, &val) < 0)
+				return -EINVAL;
+			wprobe_data->count = val;
+		}
+	}

This handles count option, but

[...]

+	ret = event_trigger_parse_num(param, trigger_data);
+	if (ret)
+		return ret;

Here we parse the count again. However, this trigger_data->count
is ignored.

I think the new wprobe_trigger_data->count is redundant. it should
use trigger_data->count.

Thank you,

-- 
Masami Hiramatsu (Google) [off-list ref]