[PATCH v5 5/6] ftrace: Update the mcount_loc check of skipped entries

[Steven Rostedt <rostedt@goodmis.org>]

From: Steven Rostedt <rostedt@goodmis.org>

Now that weak functions turn into skipped entries, update the check to
make sure the amount that was allocated would fit both the entries that
were allocated as well as those that were skipped.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v4: https://lore.kernel.org/20250217153453.792481985@goodmis.org

- Initialized variable "remaining" to zero

 kernel/trace/ftrace.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index e3f89924f603..e657013424aa 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7111,7 +7111,28 @@ static int ftrace_process_locs(struct module *mod,
 
 	/* We should have used all pages unless we skipped some */
 	if (pg_unuse) {
-		WARN_ON(!skipped);
+		unsigned long pg_remaining, remaining = 0;
+		unsigned long skip;
+
+		/* Count the number of entries unused and compare it to skipped. */
+		pg_remaining = (ENTRIES_PER_PAGE << pg->order) - pg->index;
+
+		if (!WARN(skipped < pg_remaining, "Extra allocated pages for ftrace")) {
+
+			skip = skipped - pg_remaining;
+
+			for (pg = pg_unuse; pg; pg = pg->next)
+				remaining += 1 << pg->order;
+
+			skip = DIV_ROUND_UP(skip, ENTRIES_PER_PAGE);
+
+			/*
+			 * Check to see if the number of pages remaining would
+			 * just fit the number of entries skipped.
+			 */
+			WARN(skip != remaining, "Extra allocated pages for ftrace: %lu with %lu skipped",
+			     remaining, skipped);
+		}
 		/* Need to synchronize with ftrace_location_range() */
 		synchronize_rcu();
 		ftrace_free_pages(pg_unuse);
-- 
2.47.2