On 16/01/2025 11:08 am, Kuan-Wei Chiu wrote:
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@xxxxxxxxxxxxxxx Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx> --- Changes in v3: - Perform a full comparison for clarity, as suggested by James.
Reviewed-by: James Clark <james.clark@xxxxxxxxxx>
