From 02e3024175274ed4bf7912e7a1281b300cec76b5 Mon Sep 17 00:00:00 2001 From: Neeraj Upadhyay Date: Sat, 11 Dec 2021 22:31:39 +0530 Subject: rcu/nocb: Handle concurrent nocb kthreads creation When multiple CPUs in the same nocb gp/cb group concurrently come online, they might try to concurrently create the same rcuog kthread. Fix this by using nocb gp CPU's spawn mutex to provide mutual exclusion for the rcuog kthread creation code. [ paulmck: Whitespace fixes per kernel test robot feedback. ] Acked-by: David Woodhouse Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_nocb.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'kernel/rcu/tree_nocb.h') diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index eeafb546a7a0..1e40519d1a05 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1226,6 +1226,7 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) raw_spin_lock_init(&rdp->nocb_gp_lock); timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0); rcu_cblist_init(&rdp->nocb_bypass); + mutex_init(&rdp->nocb_gp_kthread_mutex); } /* @@ -1248,13 +1249,17 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) /* If we didn't spawn the GP kthread first, reorganize! */ rdp_gp = rdp->nocb_gp_rdp; + mutex_lock(&rdp_gp->nocb_gp_kthread_mutex); if (!rdp_gp->nocb_gp_kthread) { t = kthread_run(rcu_nocb_gp_kthread, rdp_gp, "rcuog/%d", rdp_gp->cpu); - if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) + if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) { + mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); return; + } WRITE_ONCE(rdp_gp->nocb_gp_kthread, t); } + mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); /* Spawn the kthread for this CPU. */ t = kthread_run(rcu_nocb_cb_kthread, rdp, -- cgit v1.2.3-70-g09d2