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When calloc() fails, the > function returns without writing @stats. > > The caller in main() declares acc_stats uninitialized, passes it as > the @stats argument, and then reads it unconditionally: > > __u64 acc_stats[FCG_NR_STATS]; > fcg_read_stats(skel, acc_stats); > stats[i] = acc_stats[i] - last_stats[i]; // reads garbage > > Because fcg_read_stats() returns void, the caller cannot detect the > failure. Reading the uninitialized array is undefined behavior, and > the garbage is further copied into last_stats via memcpy(), corrupting > the baseline used by the next interval. > > This regression was introduced by commit cabd76bbc036 ("tools/sched_ext: > scx_flatcg: fix potential stack overflow from VLA in fcg_read_stats"), > which replaced the VLA with calloc() and inserted the failure check > before the existing memset(). > > Move the memset() above the calloc() failure check so @stats is always > zeroed regardless of allocation outcome. > > Fixes: cabd76bbc036 ("tools/sched_ext: scx_flatcg: fix potential stack overflow from VLA in fcg_read_stats") > Signed-off-by: Liang Luo Makes sense. Reviewed-by: Andrea Righi Thanks, -Andrea > --- > tools/sched_ext/scx_flatcg.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/tools/sched_ext/scx_flatcg.c b/tools/sched_ext/scx_flatcg.c > index de2bef86d64d..7799782b76d1 100644 > --- a/tools/sched_ext/scx_flatcg.c > +++ b/tools/sched_ext/scx_flatcg.c > @@ -105,12 +105,12 @@ static void fcg_read_stats(struct scx_flatcg *skel, __u64 *stats) > __u64 *cnts; > __u32 idx; > > + memset(stats, 0, sizeof(stats[0]) * FCG_NR_STATS); > + > cnts = calloc(skel->rodata->nr_cpus, sizeof(__u64)); > if (!cnts) > return; > > - memset(stats, 0, sizeof(stats[0]) * FCG_NR_STATS); > - > for (idx = 0; idx < FCG_NR_STATS; idx++) { > int ret, cpu; > > -- > 2.43.0 >