linux-kernel - [PATCH] tracing: Fix cmp_entries_dup() to respect sort() comparison rules

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Message-Id: <20241203202228.1274403-1-visitorckw@gmail.com>
Date: Wed,  4 Dec 2024 04:22:28 +0800
From: Kuan-Wei Chiu <visitorckw@...il.com>
To: rostedt@...dmis.org,
	mhiramat@...nel.org
Cc: mathieu.desnoyers@...icios.com,
	namhyung@...nel.org,
	tom.zanussi@...ux.intel.com,
	jserv@...s.ncku.edu.tw,
	chuang@...nycu.edu.tw,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	Kuan-Wei Chiu <visitorckw@...il.com>,
	stable@...r.kernel.org
Subject: [PATCH] tracing: Fix cmp_entries_dup() to respect sort() comparison rules

The cmp_entries_dup() function used as the comparator for sort()
violated the symmetry and transitivity properties required by the
sorting algorithm. Specifically, it returned 1 whenever memcmp() was
non-zero, which broke the following expectations:

* Symmetry: If x < y, then y > x.
* Transitivity: If x < y and y < z, then x < z.

These violations could lead to incorrect sorting and failure to
correctly identify duplicate elements.

Fix the issue by directly returning the result of memcmp(), which
adheres to the required comparison properties.

Fixes: 08d43a5fa063 ("tracing: Add lock-free tracing_map")
Cc: stable@...r.kernel.org
Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
---
 kernel/trace/tracing_map.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/kernel/trace/tracing_map.c b/kernel/trace/tracing_map.c
index 3a56e7c8aa4f..1921ade45be3 100644
--- a/kernel/trace/tracing_map.c
+++ b/kernel/trace/tracing_map.c
@@ -845,15 +845,11 @@ int tracing_map_init(struct tracing_map *map)
 static int cmp_entries_dup(const void *A, const void *B)
 {
 	const struct tracing_map_sort_entry *a, *b;
-	int ret = 0;
 
 	a = *(const struct tracing_map_sort_entry **)A;
 	b = *(const struct tracing_map_sort_entry **)B;
 
-	if (memcmp(a->key, b->key, a->elt->map->key_size))
-		ret = 1;
-
-	return ret;
+	return memcmp(a->key, b->key, a->elt->map->key_size);
 }
 
 static int cmp_entries_sum(const void *A, const void *B)
-- 
2.34.1