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

From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 6 Apr 2010 16:51:31 +0200
Subject: 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>

---
 drivers/md/raid5.c |   13 ++++++++-----
 drivers/md/raid5.h |    1 +
 2 files changed, 9 insertions(+), 5 deletions(-)

--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1418,8 +1418,9 @@ static void raid_run_ops(struct stripe_h
 	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++;
@@ -1471,7 +1472,8 @@ static void raid_run_ops(struct stripe_h
 			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 int grow_one_stripe(struct r5conf *conf)
@@ -1907,7 +1909,7 @@ static void raid5_end_write_request(stru
 }
 
 static sector_t compute_blocknr(struct stripe_head *sh, int i, int previous);
-	
+
 static void raid5_build_block(struct stripe_head *sh, int i, int previous)
 {
 	struct r5dev *dev = &sh->dev[i];
@@ -4320,7 +4322,7 @@ static void make_request(struct mddev *m
 						  previous,
 						  &dd_idx, NULL);
 		pr_debug("raid456: make_request, sector %llu logical %llu\n",
-			(unsigned long long)new_sector, 
+			(unsigned long long)new_sector,
 			(unsigned long long)logical_sector);
 
 		sh = get_active_stripe(conf, new_sector, previous,
@@ -5116,6 +5118,7 @@ static int raid5_alloc_percpu(struct r5c
 			break;
 		}
 		per_cpu_ptr(conf->percpu, cpu)->scribble = scribble;
+		spin_lock_init(&per_cpu_ptr(conf->percpu, cpu)->lock);
 	}
 #ifdef CONFIG_HOTPLUG_CPU
 	conf->cpu_notify.notifier_call = raid456_cpu_notify;
@@ -5290,7 +5293,7 @@ static int only_parity(int raid_disk, in
 			return 1;
 		break;
 	case ALGORITHM_PARITY_0_6:
-		if (raid_disk == 0 || 
+		if (raid_disk == 0 ||
 		    raid_disk == raid_disks - 1)
 			return 1;
 		break;
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -426,6 +426,7 @@ 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 */
 		void		*scribble;   /* space for constructing buffer
 					      * lists and performing address