# \[PATCH v3 05/16\] tracing/filters: Report parse error on all -EINVAL paths in filter parsing

- From: Masami Hiramatsu (Google) \<mhiramat@kernel.org\>
- Date: 2026-10-28 00:44:15 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2026/10/17814014
- Thread: https://ratatoskr.run/linux-trace-kernel/2026/10/17814009/t.md

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

Several error paths in filter parsing return -EINVAL (or -1) without
calling parse_error() to set pe->lasterr:

1. In parse_pred(), when an invalid token is encountered where a field name
   is expected (e.g., "common_pid == 1 || (common_pid == 2 && )"), len is 0
   and it returns -1 without calling parse_error().
2. In process_preds(), when !nr_preds (e.g., empty or whitespace-only
   filter), it returns -EINVAL before predicate_parse() can set
   FILT_ERR_NO_FILTER.
3. In predicate_parse(), when op_stack overflows or the jump target check
   fails, it returns -EINVAL without calling parse_error().

Because pe->lasterr remains 0 on these paths, append_filter_err() falls
back to printing an uninformative "Error: (0)" instead of reporting the
diagnostic and error position.

Call parse_error() with the appropriate error code on all of these paths.

Fixes: 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster")
Cc: <redacted>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/trace_events_filter.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 3f56e234a02c..2554120ff6d6 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -515,6 +515,8 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
 		switch (*next) {
 		case '(':					/* #2 */
 			if (top - op_stack > nr_parens) {
+				parse_error(pe, FILT_ERR_TOO_MANY_OPEN,
+					    next - str);
 				ret = -EINVAL;
 				goto out_free;
 			}
@@ -638,6 +640,7 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
 		prog[i].when_to_branch = invert;
 		/* Make sure the program always moves forward */
 		if (WARN_ON(prog[i].target <= i)) {
+			parse_error(pe, FILT_ERR_INVALID_FILTER, 0);
 			ret = -EINVAL;
 			goto out_free;
 		}
@@ -1703,8 +1706,10 @@ static int parse_pred(const char *str, void *data,
 
 	len = i - s;
 
-	if (!len)
-		return -1;
+	if (!len) {
+		parse_error(pe, FILT_ERR_INVALID_FILTER, pos + i);
+		return -EINVAL;
+	}
 
 	field_name = kmemdup_nul(str + s, len, GFP_KERNEL);
 	if (!field_name)
@@ -2296,8 +2301,10 @@ static int process_preds(struct trace_event_call *call,
 		return ret;
 	}
 
-	if (!nr_preds)
+	if (!nr_preds) {
+		parse_error(pe, FILT_ERR_NO_FILTER, 0);
 		return -EINVAL;
+	}
 
 	prog = predicate_parse(filter_string, nr_parens, nr_preds,
 			       parse_pred, call, pe);

```