linux-kernel - [PATCH] rcu: Convert rcu_state.ofl_lock to raw_spinlock

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Date:   Wed, 15 Aug 2018 17:44:05 +0200
From:   Mike Galbraith <efault@....de>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] rcu: Convert rcu_state.ofl_lock to raw_spinlock_t


1e64b15a4b10 ("rcu: Fix grace-period hangs due to race with CPU offline")
added spinlock_t ofl_lock to the rcu_state structure, then takes it with
preemption disabled during CPU offline, giving RT sleeping lock heartburn.

Convert it to raw_spinlock_t.

Signed-off-by: Mike Galbraith <efault@....de>
---
 kernel/rcu/tree.c |   12 ++++++------
 kernel/rcu/tree.h |    2 +-
 2 files changed, 7 insertions(+), 7 deletions(-)

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -111,7 +111,7 @@ struct rcu_state sname##_state = { \
 	.abbr = sabbr, \
 	.exp_mutex = __MUTEX_INITIALIZER(sname##_state.exp_mutex), \
 	.exp_wake_mutex = __MUTEX_INITIALIZER(sname##_state.exp_wake_mutex), \
-	.ofl_lock = __SPIN_LOCK_UNLOCKED(sname##_state.ofl_lock), \
+	.ofl_lock = __RAW_SPIN_LOCK_UNLOCKED(sname##_state.ofl_lock), \
 }
 
 RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
@@ -1962,13 +1962,13 @@ static bool rcu_gp_init(struct rcu_state
 	 */
 	rsp->gp_state = RCU_GP_ONOFF;
 	rcu_for_each_leaf_node(rsp, rnp) {
-		spin_lock(&rsp->ofl_lock);
+		raw_spin_lock(&rsp->ofl_lock);
 		raw_spin_lock_irq_rcu_node(rnp);
 		if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
 		    !rnp->wait_blkd_tasks) {
 			/* Nothing to do on this leaf rcu_node structure. */
 			raw_spin_unlock_irq_rcu_node(rnp);
-			spin_unlock(&rsp->ofl_lock);
+			raw_spin_unlock(&rsp->ofl_lock);
 			continue;
 		}
 
@@ -2004,7 +2004,7 @@ static bool rcu_gp_init(struct rcu_state
 		}
 
 		raw_spin_unlock_irq_rcu_node(rnp);
-		spin_unlock(&rsp->ofl_lock);
+		raw_spin_unlock(&rsp->ofl_lock);
 	}
 	rcu_gp_slow(rsp, gp_preinit_delay); /* Races with CPU hotplug. */
 
@@ -3892,7 +3892,7 @@ static void rcu_cleanup_dying_idle_cpu(i
 
 	/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
 	mask = rdp->grpmask;
-	spin_lock(&rsp->ofl_lock);
+	raw_spin_lock(&rsp->ofl_lock);
 	raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
 	rdp->rcu_ofl_gp_seq = READ_ONCE(rsp->gp_seq);
 	rdp->rcu_ofl_gp_flags = READ_ONCE(rsp->gp_flags);
@@ -3903,7 +3903,7 @@ static void rcu_cleanup_dying_idle_cpu(i
 	}
 	rnp->qsmaskinitnext &= ~mask;
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-	spin_unlock(&rsp->ofl_lock);
+	raw_spin_unlock(&rsp->ofl_lock);
 }
 
 /*
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -368,7 +368,7 @@ struct rcu_state {
 	char abbr;				/* Abbreviated name. */
 	struct list_head flavors;		/* List of RCU flavors. */
 
-	spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
+	raw_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
 						/* Synchronize offline with */
 						/*  GP pre-initialization. */
 };