[PATCH 5.5 107/151] ftrace: Return the first found result in lookup_rec()

[Greg Kroah-Hartman]

From: Artem Savkov <asavkov@xxxxxxxxxx>

commit d9815bff6b379ff46981bea9dfeb146081eab314 upstream.

It appears that ip ranges can overlap so. In that case lookup_rec()
returns whatever results it got last even if it found nothing in last
searched page.

This breaks an obscure livepatch late module patching usecase:
  - load livepatch
  - load the patched module
  - unload livepatch
  - try to load livepatch again

To fix this return from lookup_rec() as soon as it found the record
containing searched-for ip. This used to be this way prior lookup_rec()
introduction.

Link: http://lkml.kernel.org/r/20200306174317.21699-1-asavkov@xxxxxxxxxx

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 7e16f581a817 ("ftrace: Separate out functionality from ftrace_location_range()")
Signed-off-by: Artem Savkov <asavkov@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/trace/ftrace.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1552,6 +1552,8 @@ static struct dyn_ftrace *lookup_rec(uns
 		rec = bsearch(&key, pg->records, pg->index,
 			      sizeof(struct dyn_ftrace),
 			      ftrace_cmp_recs);
+		if (rec)
+			break;
 	}
 	return rec;
 }