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perf bench: Fix undefined behavior in cmpworker()

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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>
This commit is contained in:
Kuan-Wei Chiu 2025-01-16 19:08:42 +08:00 committed by Namhyung Kim
parent 035f0c279b
commit 62892e77b8
1 changed files with 6 additions and 1 deletions
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7
tools/perf/bench/epoll-wait.c
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@ -420,7 +420,12 @@ 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;
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)