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tools/sched_ext: scx_userland: fix data races on shared counters

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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 <devnexen@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
David Carlier
2026-02-18 19:22:23 +00:00
committed by Tejun Heo
parent 625be3456b
commit f892f9f994
1 changed files with 13 additions and 13 deletions
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26
tools/sched_ext/scx_userland.c
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@@ -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);