tools/sched_ext: scx_pair: fix stride == 0 crash on single-CPU systems

nr_cpu_ids / 2 produces stride 0 on a single-CPU system, which later
causes SCX_BUG_ON(i == j) to fire. Validate stride after option
parsing to also catch invalid user-supplied values via -S.

Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/tools/sched_ext/scx_pair.c b/tools/sched_ext/scx_pair.c
index d3e97fa..2a82d8a 100644 (file)
--- a/tools/sched_ext/scx_pair.c
+++ b/tools/sched_ext/scx_pair.c
@@ -56,7 +56,6 @@ restart:
        skel = SCX_OPS_OPEN(pair_ops, scx_pair);
 
        skel->rodata->nr_cpu_ids = libbpf_num_possible_cpus();
-       assert(skel->rodata->nr_cpu_ids > 0);
        skel->rodata->pair_batch_dur_ns = __COMPAT_ENUM_OR_ZERO("scx_public_consts", "SCX_SLICE_DFL");
 
        /* pair up the earlier half to the latter by default, override with -s */
@@ -76,6 +75,12 @@ restart:
                }
        }
 
+       /* Stride must be positive to pair distinct CPUs. */
+       if (stride <= 0) {
+               fprintf(stderr, "Invalid stride %d, must be positive\n", stride);
+               scx_pair__destroy(skel);
+               return -1;
+       }
        bpf_map__set_max_entries(skel->maps.pair_ctx, skel->rodata->nr_cpu_ids / 2);
 
        /* Resize arrays so their element count is equal to cpu count. */