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commit62892e77b8upstream. 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:121dd9ea01("perf bench: Add epoll parallel epoll_wait benchmark") Cc: stable@vger.kernel.org Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com> Reviewed-by: James Clark <james.clark@linaro.org> Link: https://lore.kernel.org/r/20250116110842.4087530-1-visitorckw@gmail.com Signed-off-by: Namhyung Kim <namhyung@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>