From 02e3024175274ed4bf7912e7a1281b300cec76b5 Mon Sep 17 00:00:00 2001 From: Neeraj Upadhyay Date: Sat, 11 Dec 2021 22:31:39 +0530 Subject: [PATCH] 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.h | 2 ++ kernel/rcu/tree_nocb.h | 7 ++++++- 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 486fc901bd08..24dd4b0d805f 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -203,6 +203,8 @@ struct rcu_data { int nocb_defer_wakeup; /* Defer wakeup of nocb_kthread. */ struct timer_list nocb_timer; /* Enforce finite deferral. */ unsigned long nocb_gp_adv_time; /* Last call_rcu() CB adv (jiffies). */ + struct mutex nocb_gp_kthread_mutex; /* Exclusion for nocb gp kthread */ + /* spawning */ /* The following fields are used by call_rcu, hence own cacheline. */ raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp; 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,