linux-kernel - [PATCH] perf bench: Fix undefined behavior in cmpworker()

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Message-Id: <20241209145728.1975311-1-visitorckw@gmail.com>
Date: Mon,  9 Dec 2024 22:57:28 +0800
From: Kuan-Wei Chiu <visitorckw@...il.com>
To: peterz@...radead.org,
	mingo@...hat.com,
	acme@...nel.org,
	namhyung@...nel.org
Cc: mark.rutland@....com,
	alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org,
	irogers@...gle.com,
	adrian.hunter@...el.com,
	kan.liang@...ux.intel.com,
	jserv@...s.ncku.edu.tw,
	chuang@...nycu.edu.tw,
	dave@...olabs.net,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Kuan-Wei Chiu <visitorckw@...il.com>,
	stable@...r.kernel.org
Subject: [PATCH] perf bench: Fix undefined behavior in cmpworker()

The comparison function cmpworker() does not comply with the C
standard's requirements for qsort() comparison functions. Specifically,
it returns 0 when w1->tid < w2->tid, which is incorrect. According to
the standard, the function must return a negative value in such cases
to preserve proper ordering.

This violation causes undefined behavior, potentially leading to issues
such as memory corruption in certain versions of glibc [1].

Fix the issue by returning -1 when w1->tid < w2->tid, ensuring
compliance with the C standard and preventing undefined behavior.

Link: https://www.qualys.com/2024/01/30/qsort.txt [1]
Fixes: 121dd9ea0116 ("perf bench: Add epoll parallel epoll_wait benchmark")
Cc: stable@...r.kernel.org
Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
---
 tools/perf/bench/epoll-wait.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/bench/epoll-wait.c b/tools/perf/bench/epoll-wait.c
index ef5c4257844d..4868d610e9bf 100644
--- a/tools/perf/bench/epoll-wait.c
+++ b/tools/perf/bench/epoll-wait.c
@@ -420,7 +420,7 @@ static int cmpworker(const void *p1, const void *p2)
 
 	struct worker *w1 = (struct worker *) p1;
 	struct worker *w2 = (struct worker *) p2;
-	return w1->tid > w2->tid;
+	return w1->tid > w2->tid ? 1 : -1;
 }
 
 int bench_epoll_wait(int argc, const char **argv)
-- 
2.34.1