dm-buffered: fix a bug when calling memcpy

Fix a bug if the buffer is allocated using __vmalloc or if it is allocated
from slab cache.

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

---
 drivers/md/dm-buffered-target.c |   23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

Index: linux-2.6/drivers/md/dm-buffered-target.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-buffered-target.c
+++ linux-2.6/drivers/md/dm-buffered-target.c
@@ -76,18 +76,6 @@ static sector_t _buffered_size(struct dm
 	return _to_block(bc, ti->len - bc->start) + (_sector_mod(bc, ti->len) ? 1 : 0);
 }
 
-static void _memcpy(struct buffered_c *bc, struct dm_buffer *bp,
-		    struct page *dst, struct page *src,
-		    loff_t dst_offset, loff_t src_offset, size_t len)
-{
-	void *d = kmap_local_page(dst);
-	void *s = kmap_local_page(src);
-
-	memcpy(d + dst_offset, s + src_offset, len);
-	kunmap_local(d);
-	kunmap_local(s);
-}
-
 /*
  * Process @bvec of @bio optionally doing 2 bufio I/Os
  * in case the page of the bio_vec overlaps two buffers.
@@ -103,6 +91,7 @@ static void _io(struct buffered_c *bc, s
 	struct dm_buffer *bp;
 
 	while (total_len) {
+		char *p;
 		block = _to_block(bc, sector);
 		buffer_offset = to_bytes(_sector_mod(bc, sector));
 		len = min(block_size - buffer_offset, total_len);
@@ -137,8 +126,10 @@ static void _io(struct buffered_c *bc, s
 			WARN_ON_ONCE(block != dm_bufio_get_block_number(bp));
 			/* Superfluous call to cover the API example */
 			buffer = dm_bufio_get_block_data(bp);
-			_memcpy(bc, bp, virt_to_page(buffer), bvec->bv_page,
-				buffer_offset, bvec_offset, len);
+
+			p = kmap_local_page(bvec->bv_page);
+			memcpy(buffer + buffer_offset, p + bvec_offset, len);
+			kunmap_local(p);
 
 			/* Superfluous conditional to show both functions dirtying buffers. */
 			if (!buffer_offset && len == block_size)
@@ -150,8 +141,8 @@ static void _io(struct buffered_c *bc, s
 		} else {
 			/* (Superfluous) function consistency check example */
 			WARN_ON(block != dm_bufio_get_block_number(bp));
-			_memcpy(bc, bp, bvec->bv_page, virt_to_page(buffer),
-				bvec_offset, buffer_offset, len);
+			p = kmap_local_page(bvec->bv_page);
+			memcpy(p + bvec_offset, buffer + buffer_offset, len);
 			dm_bufio_release(bp);
 		}