From f892f9f99464bead942a75d2b00dda6be07de97f Mon Sep 17 00:00:00 2001 From: David Carlier Date: Wed, 18 Feb 2026 19:22:23 +0000 Subject: tools/sched_ext: scx_userland: fix data races on shared counters The stats thread reads nr_vruntime_enqueues, nr_vruntime_dispatches, nr_vruntime_failed, and nr_curr_enqueued concurrently with the main thread writing them, with no synchronization. Use __atomic builtins with relaxed ordering for all accesses to these counters to eliminate the data races. Only display accuracy is affected, not scheduling correctness. Signed-off-by: David Carlier Signed-off-by: Tejun Heo --- tools/sched_ext/scx_userland.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-) diff --git a/tools/sched_ext/scx_userland.c b/tools/sched_ext/scx_userland.c index 504a80824f5c..3f2aba658b4a 100644 --- a/tools/sched_ext/scx_userland.c +++ b/tools/sched_ext/scx_userland.c @@ -157,9 +157,9 @@ static int dispatch_task(__s32 pid) err = bpf_map_update_elem(dispatched_fd, NULL, &pid, 0); if (err) { - nr_vruntime_failed++; + __atomic_add_fetch(&nr_vruntime_failed, 1, __ATOMIC_RELAXED); } else { - nr_vruntime_dispatches++; + __atomic_add_fetch(&nr_vruntime_dispatches, 1, __ATOMIC_RELAXED); } return err; @@ -202,8 +202,8 @@ static int vruntime_enqueue(const struct scx_userland_enqueued_task *bpf_task) return ENOENT; update_enqueued(curr, bpf_task); - nr_vruntime_enqueues++; - nr_curr_enqueued++; + __atomic_add_fetch(&nr_vruntime_enqueues, 1, __ATOMIC_RELAXED); + __atomic_add_fetch(&nr_curr_enqueued, 1, __ATOMIC_RELAXED); /* * Enqueue the task in a vruntime-sorted list. A more optimal data @@ -279,9 +279,9 @@ static void dispatch_batch(void) LIST_INSERT_HEAD(&vruntime_head, task, entries); break; } - nr_curr_enqueued--; + __atomic_sub_fetch(&nr_curr_enqueued, 1, __ATOMIC_RELAXED); } - skel->bss->nr_scheduled = nr_curr_enqueued; + skel->bss->nr_scheduled = __atomic_load_n(&nr_curr_enqueued, __ATOMIC_RELAXED); } static void *run_stats_printer(void *arg) @@ -306,9 +306,9 @@ static void *run_stats_printer(void *arg) printf("|-----------------------|\n"); printf("| VRUNTIME / USER |\n"); printf("|-----------------------|\n"); - printf("| enq: %10llu |\n", nr_vruntime_enqueues); - printf("| disp: %10llu |\n", nr_vruntime_dispatches); - printf("| failed: %10llu |\n", nr_vruntime_failed); + printf("| enq: %10llu |\n", __atomic_load_n(&nr_vruntime_enqueues, __ATOMIC_RELAXED)); + printf("| disp: %10llu |\n", __atomic_load_n(&nr_vruntime_dispatches, __ATOMIC_RELAXED)); + printf("| failed: %10llu |\n", __atomic_load_n(&nr_vruntime_failed, __ATOMIC_RELAXED)); printf("o-----------------------o\n"); printf("\n\n"); fflush(stdout); @@ -376,10 +376,10 @@ static void bootstrap(char *comm) { exit_req = 0; min_vruntime = 0.0; - nr_vruntime_enqueues = 0; - nr_vruntime_dispatches = 0; - nr_vruntime_failed = 0; - nr_curr_enqueued = 0; + __atomic_store_n(&nr_vruntime_enqueues, 0, __ATOMIC_RELAXED); + __atomic_store_n(&nr_vruntime_dispatches, 0, __ATOMIC_RELAXED); + __atomic_store_n(&nr_vruntime_failed, 0, __ATOMIC_RELAXED); + __atomic_store_n(&nr_curr_enqueued, 0, __ATOMIC_RELAXED); memset(tasks, 0, pid_max * sizeof(*tasks)); LIST_INIT(&vruntime_head); -- cgit v1.2.3