5.4-stable review patch. If anyone has any objections, please let me know.
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From: Kuan-Wei Chiu visitorckw@gmail.com
commit 62892e77b8a64b9dc0e1da75980aa145347b6820 upstream.
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 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 --- tools/perf/bench/epoll-wait.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
--- a/tools/perf/bench/epoll-wait.c +++ b/tools/perf/bench/epoll-wait.c @@ -407,7 +407,12 @@ static int cmpworker(const void *p1, con
struct worker *w1 = (struct worker *) p1; struct worker *w2 = (struct worker *) p2; - return w1->tid > w2->tid; + + if (w1->tid > w2->tid) + return 1; + if (w1->tid < w2->tid) + return -1; + return 0; }
int bench_epoll_wait(int argc, const char **argv)