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The race occurs between bpf_scx_unreg() and a concurrent reg(): 1. Thread A's bpf_scx_unreg() calls scx_disable() then kthread_flush_work(), which blocks until disable completes and transitions state back to SCX_DISABLED. 2. With state SCX_DISABLED, a concurrent reg() allocates a new sch_B and sets ops->priv = sch_B under scx_enable_mutex. 3. Thread A's bpf_scx_unreg() then executes RCU_INIT_POINTER(ops->priv, NULL), overwriting sch_B. 4. When Thread B's link is destroyed, bpf_scx_unreg() reads ops->priv == NULL and passes it to scx_disable(), which calls scx_claim_exit(NULL), crashing at NULL+0x310. Fix by adding a NULL guard for the case where ops->priv was never set, and by acquiring scx_enable_mutex before clearing ops->priv so that the check-and-clear is atomic with respect to reg() which also sets ops->priv under scx_enable_mutex. Signed-off-by: zhidao su --- kernel/sched/ext.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 551bfb99157d..01077cc2eb62 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -7372,9 +7372,22 @@ static void bpf_scx_unreg(void *kdata, struct bpf_link *link) struct sched_ext_ops *ops = kdata; struct scx_sched *sch = rcu_dereference_protected(ops->priv, true); + if (!sch) + return; + scx_disable(sch, SCX_EXIT_UNREG); kthread_flush_work(&sch->disable_work); - RCU_INIT_POINTER(ops->priv, NULL); + + /* + * A concurrent reg() may have already installed a new scheduler into + * ops->priv by the time disable completes. Clear ops->priv only if it + * still holds our sch. + */ + mutex_lock(&scx_enable_mutex); + if (rcu_access_pointer(ops->priv) == sch) + RCU_INIT_POINTER(ops->priv, NULL); + mutex_unlock(&scx_enable_mutex); + kobject_put(&sch->kobj); } -- 2.43.0