patches/md-raid5-percpu-handling-rt-aware.patch

From 77ca2d089e33408695e05a2d506241513dffc365 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 6 Apr 2010 16:51:31 +0200
Subject: [PATCH] md: raid5: Make raid5_percpu handling RT aware

__raid_run_ops() disables preemption with get_cpu() around the access
to the raid5_percpu variables. That causes scheduling while atomic
spews on RT.

Serialize the access to the percpu data with a lock and keep the code
preemptible.

Reported-by: Udo van den Heuvel <udovdh@xs4all.nl>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Udo van den Heuvel <udovdh@xs4all.nl>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 2e38cfac5b1d..a6fd1ce1d524 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2058,8 +2058,9 @@ static void raid_run_ops(struct stripe_head *sh, unsigned long ops_request)
 	struct raid5_percpu *percpu;
 	unsigned long cpu;
 
-	cpu = get_cpu();
+	cpu = get_cpu_light();
 	percpu = per_cpu_ptr(conf->percpu, cpu);
+	spin_lock(&percpu->lock);
 	if (test_bit(STRIPE_OP_BIOFILL, &ops_request)) {
 		ops_run_biofill(sh);
 		overlap_clear++;
@@ -2118,7 +2119,8 @@ static void raid_run_ops(struct stripe_head *sh, unsigned long ops_request)
 			if (test_and_clear_bit(R5_Overlap, &dev->flags))
 				wake_up(&sh->raid_conf->wait_for_overlap);
 		}
-	put_cpu();
+	spin_unlock(&percpu->lock);
+	put_cpu_light();
 }
 
 static void free_stripe(struct kmem_cache *sc, struct stripe_head *sh)
@@ -6758,6 +6760,7 @@ static int raid456_cpu_up_prepare(unsigned int cpu, struct hlist_node *node)
 			__func__, cpu);
 		return -ENOMEM;
 	}
+	spin_lock_init(&per_cpu_ptr(conf->percpu, cpu)->lock);
 	return 0;
 }
 
@@ -6768,7 +6771,6 @@ static int raid5_alloc_percpu(struct r5conf *conf)
 	conf->percpu = alloc_percpu(struct raid5_percpu);
 	if (!conf->percpu)
 		return -ENOMEM;
-
 	err = cpuhp_state_add_instance(CPUHP_MD_RAID5_PREPARE, &conf->node);
 	if (!err) {
 		conf->scribble_disks = max(conf->raid_disks,
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 625c7f16fd6b..87991db86e18 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -613,6 +613,7 @@ struct r5conf {
 	int			recovery_disabled;
 	/* per cpu variables */
 	struct raid5_percpu {
+		spinlock_t	lock;		/* Protection for -RT */
 		struct page	*spare_page; /* Used when checking P/Q in raid6 */
 		struct flex_array *scribble;   /* space for constructing buffer
 					      * lists and performing address
-- 
2.1.4