linux-kernel - [PATCH] ftrace: return first found result in lookup

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Message-Id: <20200306081035.21213-1-asavkov@redhat.com>
Date:   Fri,  6 Mar 2020 09:10:35 +0100
From:   Artem Savkov <asavkov@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        Artem Savkov <asavkov@...hat.com>
Subject: [PATCH] ftrace: return first found result in lookup_rec()

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.

Fixes: 7e16f581a817 ("ftrace: Separate out functionality from ftrace_location_range()")
Signed-off-by: Artem Savkov <asavkov@...hat.com>
---
 kernel/trace/ftrace.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3f7ee102868a..b0f5ee1fd6e4 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1547,8 +1547,10 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
 		rec = bsearch(&key, pg->records, pg->index,
 			      sizeof(struct dyn_ftrace),
 			      ftrace_cmp_recs);
+		if (rec)
+			return rec;
 	}
-	return rec;
+	return NULL;
 }
 
 /**
-- 
2.21.1