From 8434706bf04a30eeccf096e0b2dd27040a1c3f4b 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. Signed-off-by: Neeraj Upadhyay Signed-off-by: David Woodhouse --- 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 055e30b3e5e0d..d7785f569a4e6 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -210,6 +210,8 @@ 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 368ef7b9af4fe..1ad54b2336e6a 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1171,6 +1171,7 @@ 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); } /* @@ -1193,13 +1194,17 @@ static void rcu_spawn_one_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, -- 2.50.1