rcu/nocb: Fix possible invalid rdp's->nocb_cb_kthread pointer access

[ Upstream commit 1bba3900ca18bdae28d1b9fa10f16a8f8cb2ada1 ]

In the preparation stage of CPU online, if the corresponding
the rdp's->nocb_cb_kthread does not exist, will be created,
there is a situation where the rdp's rcuop kthreads creation fails,
and then de-offload this CPU's rdp, does not assign this CPU's
rdp->nocb_cb_kthread pointer, but this rdp's->nocb_gp_rdp and
rdp's->rdp_gp->nocb_gp_kthread is still valid.

This will cause the subsequent re-offload operation of this offline
CPU, which will pass the conditional check and the kthread_unpark()
will access invalid rdp's->nocb_cb_kthread pointer.

This commit therefore use rdp's->nocb_gp_kthread instead of
rdp_gp's->nocb_gp_kthread for safety check.

Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 2ad3a88623a7c43bd62cbfc931562562faad848f..a1a5942d70170bb4f0a829ab217ded19a627f136 100644 (file)
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1152,7 +1152,6 @@ static bool rcu_nocb_rdp_offload_wait_cond(struct rcu_data *rdp)
 static int rcu_nocb_rdp_offload(struct rcu_data *rdp)
 {
        int wake_gp;
-       struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
 
        WARN_ON_ONCE(cpu_online(rdp->cpu));
        /*
@@ -1162,7 +1161,7 @@ static int rcu_nocb_rdp_offload(struct rcu_data *rdp)
        if (!rdp->nocb_gp_rdp)
                return -EINVAL;
 
-       if (WARN_ON_ONCE(!rdp_gp->nocb_gp_kthread))
+       if (WARN_ON_ONCE(!rdp->nocb_gp_kthread))
                return -EINVAL;
 
        pr_info("Offloading %d\n", rdp->cpu);
@@ -1172,7 +1171,7 @@ static int rcu_nocb_rdp_offload(struct rcu_data *rdp)
 
        wake_gp = rcu_nocb_queue_toggle_rdp(rdp);
        if (wake_gp)
-               wake_up_process(rdp_gp->nocb_gp_kthread);
+               wake_up_process(rdp->nocb_gp_kthread);
 
        swait_event_exclusive(rdp->nocb_state_wq,
                              rcu_nocb_rdp_offload_wait_cond(rdp));