Index: linux-2.6.27.21-0.1/fs/ext4/extents.c
===================================================================
--- linux-2.6.27.21-0.1.orig/fs/ext4/extents.c	2009-06-19 15:50:57.000000000 +0530
+++ linux-2.6.27.21-0.1/fs/ext4/extents.c	2009-06-19 15:56:32.000000000 +0530
@@ -1736,11 +1736,13 @@
 {
 	struct ext4_ext_cache *cex;
 	BUG_ON(len == 0);
+	spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
 	cex = &EXT4_I(inode)->i_cached_extent;
 	cex->ec_type = type;
 	cex->ec_block = block;
 	cex->ec_len = len;
 	cex->ec_start = start;
+	spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
 }
 
 /*
@@ -1797,12 +1799,17 @@
 			struct ext4_extent *ex)
 {
 	struct ext4_ext_cache *cex;
+	int ret = EXT4_EXT_CACHE_NO;
 
+	/*
+	 * We borrow i_block_reservation_lock to protect i_cached_extent
+	 */
+	spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
 	cex = &EXT4_I(inode)->i_cached_extent;
 
 	/* has cache valid data? */
 	if (cex->ec_type == EXT4_EXT_CACHE_NO)
-		return EXT4_EXT_CACHE_NO;
+		goto errout;
 
 	BUG_ON(cex->ec_type != EXT4_EXT_CACHE_GAP &&
 			cex->ec_type != EXT4_EXT_CACHE_EXTENT);
@@ -1813,11 +1820,12 @@
 		ext_debug("%u cached by %u:%u:%llu\n",
 				block,
 				cex->ec_block, cex->ec_len, cex->ec_start);
-		return cex->ec_type;
+		ret = cex->ec_type;
 	}
 
-	/* not in cache */
-	return EXT4_EXT_CACHE_NO;
+errout:
+	spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
+	return ret;
 }
 
 /*