# \[PATCH v2 2/9\] ftrace: Let ftrace\_call\_adjust() reject a patch site

- From: Jose Fernandez (Anthropic) \<hidden\>
- Date: 2026-09-24 22:36:33 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2026/09/17639556
- Thread: https://ratatoskr.run/live-patching/2026/09/17639554/t.md

```text
When ftrace_call_adjust() returns 0 for a patch site,
ftrace_process_locs() does not skip the site. The NULL test runs before
the adjustment since commit 6eeca746fa5f ("ftrace: Test mcount_loc
addr before calling ftrace_call_addr()"), so the 0 is stored as the
record's ip and ftrace_init_nop() later hits the BUG_ON() in arm64's
patch_map(). Test the adjusted address too and count the site as
skipped.

Reviewed-by: Ben Cressey <redacted>
Reviewed-by: Florent Revest (Anthropic) <redacted>
Assisted-by: LLM
Signed-off-by: Jose Fernandez (Anthropic) <redacted>
---
 kernel/trace/ftrace.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 2cc2d41353c10..fa541d3e8784a 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7676,6 +7676,11 @@ static int ftrace_process_locs(struct module *mod,
 		}
 
 		addr = ftrace_call_adjust(addr);
+		/* The architecture may return 0 to reject a patch site */
+		if (!addr) {
+			skipped++;
+			continue;
+		}
 
 		end_offset = (pg->index+1) * sizeof(pg->records[0]);
 		if (end_offset > PAGE_SIZE << pg->order) {

-- 
2.52.0

```