diff options
| author | Kuan-Wei Chiu <visitorckw@gmail.com> | 2025-01-16 19:08:42 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-03-13 12:50:26 +0100 |
| commit | a0d751d2d8ecd500e303f2d9fe7b35ad2c892221 (patch) | |
| tree | 3eb5c28db14ef676cb85ba74b7d035f333bc89be | |
| parent | be042a185cc566f29dac65cc77f602deb1bce90a (diff) | |
perf bench: Fix undefined behavior in cmpworker()
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>
| -rw-r--r-- | tools/perf/bench/epoll-wait.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/tools/perf/bench/epoll-wait.c b/tools/perf/bench/epoll-wait.c index 79d13dbc0a47..110d67586373 100644 --- a/tools/perf/bench/epoll-wait.c +++ b/tools/perf/bench/epoll-wait.c @@ -406,7 +406,12 @@ 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) |