dm optimization: don't disable irq when taking map_lock

It is supposed that no one will take dm table from the interrupt context.
No one can submit bios from the interrupt context anyway, so we suppose that
no one will call I/O helper functions from interrupt context.
This patch removes irq disabling from device mapper.

The patch adds BUG_ON(in_interrupt()) to catch parts of code that may
possibly take dm table from an interrupt context.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm.c |   16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

Index: linux-3.3-devel/drivers/md/dm.c
===================================================================
--- linux-3.3-devel.orig/drivers/md/dm.c	2012-04-17 22:33:31.000000000 +0200
+++ linux-3.3-devel/drivers/md/dm.c	2012-04-17 22:35:07.000000000 +0200
@@ -546,13 +546,13 @@ static void queue_io(struct mapped_devic
 struct dm_table *dm_get_live_table(struct mapped_device *md)
 {
 	struct dm_table *t;
-	unsigned long flags;
 
-	read_lock_irqsave(&md->map_lock, flags);
+	BUG_ON(in_interrupt());
+	read_lock(&md->map_lock);
 	t = md->map;
 	if (t)
 		dm_table_get(t);
-	read_unlock_irqrestore(&md->map_lock, flags);
+	read_unlock(&md->map_lock);
 
 	return t;
 }
@@ -2057,7 +2057,6 @@ static struct dm_table *__bind(struct ma
 	struct dm_table *old_map;
 	struct request_queue *q = md->queue;
 	sector_t size;
-	unsigned long flags;
 	int merge_is_optional;
 
 	size = dm_table_get_size(t);
@@ -2086,7 +2085,7 @@ static struct dm_table *__bind(struct ma
 
 	merge_is_optional = dm_table_merge_is_optional(t);
 
-	write_lock_irqsave(&md->map_lock, flags);
+	write_lock(&md->map_lock);
 	old_map = md->map;
 	md->map = t;
 	md->immutable_target_type = dm_table_get_immutable_target_type(t);
@@ -2096,7 +2095,7 @@ static struct dm_table *__bind(struct ma
 		set_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
 	else
 		clear_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
-	write_unlock_irqrestore(&md->map_lock, flags);
+	write_unlock(&md->map_lock);
 
 	return old_map;
 }
@@ -2107,15 +2106,14 @@ static struct dm_table *__bind(struct ma
 static struct dm_table *__unbind(struct mapped_device *md)
 {
 	struct dm_table *map = md->map;
-	unsigned long flags;
 
 	if (!map)
 		return NULL;
 
 	dm_table_event_callback(map, NULL, NULL);
-	write_lock_irqsave(&md->map_lock, flags);
+	write_lock(&md->map_lock);
 	md->map = NULL;
-	write_unlock_irqrestore(&md->map_lock, flags);
+	write_unlock(&md->map_lock);
 
 	return map;
 }