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([140.113.216.168]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72d4067e682sm10679087b3a.125.2025.01.16.03.08.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Jan 2025 03:08:55 -0800 (PST) From: Kuan-Wei Chiu To: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org Cc: mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, Ching-Chun Huang , Chun-Ying Huang , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, James Clark , Kuan-Wei Chiu , stable@vger.kernel.org Subject: [PATCH v3] perf bench: Fix undefined behavior in cmpworker() Date: Thu, 16 Jan 2025 19:08:42 +0800 Message-Id: <20250116110842.4087530-1-visitorckw@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The comparison function cmpworker() violates the C standard's requirements for qsort() comparison functions, which mandate symmetry and transitivity: Symmetry: If x < y, then y > x. Transitivity: If x < y and y < z, then x < z. In its current implementation, cmpworker() incorrectly returns 0 when w1->tid < w2->tid, which breaks both symmetry and transitivity. This violation causes undefined behavior, potentially leading to issues such as memory corruption in 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@vger.kernel.org Signed-off-by: Kuan-Wei Chiu Reviewed-by: James Clark --- Changes in v3: - Perform a full comparison for clarity, as suggested by James. tools/perf/bench/epoll-wait.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/tools/perf/bench/epoll-wait.c b/tools/perf/bench/epoll-wait.c index ef5c4257844d..20fe4f72b4af 100644 --- a/tools/perf/bench/epoll-wait.c +++ b/tools/perf/bench/epoll-wait.c @@ -420,7 +420,12 @@ static int cmpworker(const void *p1, const void *p2) =20 struct worker *w1 =3D (struct worker *) p1; struct worker *w2 =3D (struct worker *) p2; - return w1->tid > w2->tid; + + if (w1->tid > w2->tid) + return 1; + if (w1->tid < w2->tid) + return -1; + return 0; } =20 int bench_epoll_wait(int argc, const char **argv) --=20 2.34.1