diff options
| author | zhidao su <suzhidao@xiaomi.com> | 2026-03-02 17:14:39 +0800 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2026-03-02 07:23:00 -1000 |
| commit | 9adfcef334bf9c6ef68eaecfca5f45d18614efe0 (patch) | |
| tree | a794e00eaef9d0f53c472505bd6d77d116bae33d /kernel | |
| parent | 032e084f0d43fda78c33abfc704ac13a0891a6e7 (diff) | |
sched_ext: Use READ_ONCE() for the read side of dsq->nr update
scx_bpf_dsq_nr_queued() reads dsq->nr via READ_ONCE() without holding
any lock, making dsq->nr a lock-free concurrently accessed variable.
However, dsq_mod_nr(), the sole writer of dsq->nr, only uses
WRITE_ONCE() on the write side without the matching READ_ONCE() on the
read side:
WRITE_ONCE(dsq->nr, dsq->nr + delta);
^^^^^^^
plain read -- KCSAN data race
The KCSAN documentation requires that if one accessor uses READ_ONCE()
or WRITE_ONCE() on a variable to annotate lock-free access, all other
accesses must also use the appropriate accessor. A plain read on the
right-hand side of WRITE_ONCE() leaves the pair incomplete and will
trigger KCSAN warnings.
Fix by using READ_ONCE() for the read side of the update:
WRITE_ONCE(dsq->nr, READ_ONCE(dsq->nr) + delta);
This is consistent with scx_bpf_dsq_nr_queued() and makes the
concurrent access annotation complete and KCSAN-clean.
Signed-off-by: zhidao su <suzhidao@xiaomi.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/ext.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 9280381f8923..4c2cf0d7d495 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -976,8 +976,12 @@ static bool scx_dsq_priq_less(struct rb_node *node_a, static void dsq_mod_nr(struct scx_dispatch_q *dsq, s32 delta) { - /* scx_bpf_dsq_nr_queued() reads ->nr without locking, use WRITE_ONCE() */ - WRITE_ONCE(dsq->nr, dsq->nr + delta); + /* + * scx_bpf_dsq_nr_queued() reads ->nr without locking. Use READ_ONCE() + * on the read side and WRITE_ONCE() on the write side to properly + * annotate the concurrent lockless access and avoid KCSAN warnings. + */ + WRITE_ONCE(dsq->nr, READ_ONCE(dsq->nr) + delta); } static void refill_task_slice_dfl(struct scx_sched *sch, struct task_struct *p) |