[PATCH v3 2/4] brd: extend the rcu regions to cover read and write

[Mikulas Patocka <mpatocka@redhat.com>]

This patch extends the rcu regions, so that lookup followed by a read or
write of a page is done inside rcu read lock. This is needed for the
following patch that enables discard.

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

---
 drivers/block/brd.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: linux-2.6/drivers/block/brd.c
===================================================================
--- linux-2.6.orig/drivers/block/brd.c
+++ linux-2.6/drivers/block/brd.c
@@ -150,23 +150,27 @@ static void copy_to_brd(struct brd_devic
 	size_t copy;
 
 	copy = min_t(size_t, n, PAGE_SIZE - offset);
+	rcu_read_lock();
 	page = brd_lookup_page(brd, sector);
 	BUG_ON(!page);
 
 	dst = kmap_atomic(page);
 	memcpy(dst + offset, src, copy);
 	kunmap_atomic(dst);
+	rcu_read_unlock();
 
 	if (copy < n) {
 		src += copy;
 		sector += copy >> SECTOR_SHIFT;
 		copy = n - copy;
+		rcu_read_lock();
 		page = brd_lookup_page(brd, sector);
 		BUG_ON(!page);
 
 		dst = kmap_atomic(page);
 		memcpy(dst, src, copy);
 		kunmap_atomic(dst);
+		rcu_read_unlock();
 	}
 }
 
@@ -182,6 +186,7 @@ static void copy_from_brd(void *dst, str
 	size_t copy;
 
 	copy = min_t(size_t, n, PAGE_SIZE - offset);
+	rcu_read_lock();
 	page = brd_lookup_page(brd, sector);
 	if (page) {
 		src = kmap_atomic(page);
@@ -189,11 +194,13 @@ static void copy_from_brd(void *dst, str
 		kunmap_atomic(src);
 	} else
 		memset(dst, 0, copy);
+	rcu_read_unlock();
 
 	if (copy < n) {
 		dst += copy;
 		sector += copy >> SECTOR_SHIFT;
 		copy = n - copy;
+		rcu_read_lock();
 		page = brd_lookup_page(brd, sector);
 		if (page) {
 			src = kmap_atomic(page);
@@ -201,6 +208,7 @@ static void copy_from_brd(void *dst, str
 			kunmap_atomic(src);
 		} else
 			memset(dst, 0, copy);
+		rcu_read_unlock();
 	}
 }