--- cc1.txt	2012-07-10 06:57:21.564665577 +0300
+++ cc2.txt	2012-07-10 06:59:10.272634578 +0300
@@ -2,7 +2,7 @@
 btrfs: ffff8801cafbacc0: 00 00 63 72 06 01 00 00 00 80 00 00 00 00 00 00  ..cr............
 btrfs: ffff8801cafbacd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbace0: 35 00 00 00 00 00 00 00 30 00 d7 10 02 88 ff ff  5.......0.......
-btrfs: ffff8801cafbacf0: 13 13 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
+btrfs: ffff8801cafbacf0: 15 15 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad20: 22 1c 00 00 00 00 00 00 00 00 00 00 00 00 00 00  "...............
@@ -20,9 +20,9 @@
 btrfs: ffff8801cafbade0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbadf0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbae00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
-btrfs: ffff8801cafbae10: 90 ad fb ca 01 88 ff ff 00 00 00 00 00 00 00 00  ................
-btrfs: ffff8801cafbae20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
-btrfs: ffff8801cafbae30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
+btrfs: ffff8801cafbae10: 90 ad fb ca 01 88 ff ff 01 00 00 00 00 00 00 00  ................
+btrfs: ffff8801cafbae20: 4d 00 00 00 00 00 00 00 4e 00 00 00 00 00 00 00  M.......N.......
+btrfs: ffff8801cafbae30: 07 78 02 00 00 00 00 00 00 00 00 00 00 00 00 00  .x..............
 btrfs: ffff8801cafbae40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbae50: 00 00 00 00 00 00 00 00                          ........
 btrfs: --- end eb contents at ffff8801cafbacc0 ---
--- cc2.txt	2012-07-10 06:59:10.272634578 +0300
+++ cc3.txt	2012-07-10 06:59:10.016634663 +0300
@@ -2,7 +2,7 @@
 btrfs: ffff8801cafbacc0: 00 00 63 72 06 01 00 00 00 80 00 00 00 00 00 00  ..cr............
 btrfs: ffff8801cafbacd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbace0: 35 00 00 00 00 00 00 00 30 00 d7 10 02 88 ff ff  5.......0.......
-btrfs: ffff8801cafbacf0: 15 15 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
+btrfs: ffff8801cafbacf0: 17 17 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad20: 22 1c 00 00 00 00 00 00 00 00 00 00 00 00 00 00  "...............
--- cc3.txt	2012-07-10 06:59:10.016634663 +0300
+++ cc4.txt	2012-07-10 06:59:09.752634749 +0300
@@ -2,7 +2,7 @@
 btrfs: ffff8801cafbacc0: 00 00 63 72 06 01 00 00 00 80 00 00 00 00 00 00  ..cr............
 btrfs: ffff8801cafbacd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbace0: 35 00 00 00 00 00 00 00 30 00 d7 10 02 88 ff ff  5.......0.......
-btrfs: ffff8801cafbacf0: 17 17 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
+btrfs: ffff8801cafbacf0: 19 19 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad20: 22 1c 00 00 00 00 00 00 00 00 00 00 00 00 00 00  "...............
--- cc4.txt	2012-07-10 06:59:09.752634749 +0300
+++ cc5.txt	2012-07-10 06:59:09.504634831 +0300
@@ -2,7 +2,7 @@
 btrfs: ffff8801cafbacc0: 00 00 63 72 06 01 00 00 00 80 00 00 00 00 00 00  ..cr............
 btrfs: ffff8801cafbacd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbace0: 35 00 00 00 00 00 00 00 30 00 d7 10 02 88 ff ff  5.......0.......
-btrfs: ffff8801cafbacf0: 19 19 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
+btrfs: ffff8801cafbacf0: 1b 1b 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad20: 22 1c 00 00 00 00 00 00 00 00 00 00 00 00 00 00  "...............
--- cc5.txt	2012-07-10 06:59:09.504634831 +0300
+++ cc6.txt	2012-07-10 06:59:09.240634917 +0300
@@ -2,7 +2,7 @@
 btrfs: ffff8801cafbacc0: 00 00 63 72 06 01 00 00 00 80 00 00 00 00 00 00  ..cr............
 btrfs: ffff8801cafbacd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbace0: 35 00 00 00 00 00 00 00 30 00 d7 10 02 88 ff ff  5.......0.......
-btrfs: ffff8801cafbacf0: 1b 1b 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
+btrfs: ffff8801cafbacf0: 1d 1d 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad20: 22 1c 00 00 00 00 00 00 00 00 00 00 00 00 00 00  "...............
--- cc6.txt	2012-07-10 06:59:09.240634917 +0300
+++ cc7.txt	2012-07-10 06:59:08.944635015 +0300
@@ -2,7 +2,7 @@
 btrfs: ffff8801cafbacc0: 00 00 63 72 06 01 00 00 00 80 00 00 00 00 00 00  ..cr............
 btrfs: ffff8801cafbacd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbace0: 35 00 00 00 00 00 00 00 30 00 d7 10 02 88 ff ff  5.......0.......
-btrfs: ffff8801cafbacf0: 1d 1d 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
+btrfs: ffff8801cafbacf0: 1f 1f 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad20: 22 1c 00 00 00 00 00 00 00 00 00 00 00 00 00 00  "...............
--- cc7.txt	2012-07-10 06:59:08.944635015 +0300
+++ cc8.txt	2012-07-10 06:59:08.656635109 +0300
@@ -2,7 +2,7 @@
 btrfs: ffff8801cafbacc0: 00 00 63 72 06 01 00 00 00 80 00 00 00 00 00 00  ..cr............
 btrfs: ffff8801cafbacd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbace0: 35 00 00 00 00 00 00 00 30 00 d7 10 02 88 ff ff  5.......0.......
-btrfs: ffff8801cafbacf0: 1f 1f 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
+btrfs: ffff8801cafbacf0: 21 21 00 00 03 00 00 00 00 00 00 00 00 00 00 00  !!..............
 btrfs: ffff8801cafbad00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad20: 22 1c 00 00 00 00 00 00 00 00 00 00 00 00 00 00  "...............
--- cc8.txt	2012-07-10 06:59:08.656635109 +0300
+++ cc9.txt	2012-07-10 06:59:08.328635216 +0300
@@ -2,7 +2,7 @@
 btrfs: ffff8801cafbacc0: 00 00 63 72 06 01 00 00 00 80 00 00 00 00 00 00  ..cr............
 btrfs: ffff8801cafbacd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbace0: 35 00 00 00 00 00 00 00 30 00 d7 10 02 88 ff ff  5.......0.......
-btrfs: ffff8801cafbacf0: 21 21 00 00 03 00 00 00 00 00 00 00 00 00 00 00  !!..............
+btrfs: ffff8801cafbacf0: 23 23 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ##..............
 btrfs: ffff8801cafbad00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad20: 22 1c 00 00 00 00 00 00 00 00 00 00 00 00 00 00  "...............
--- cc9.txt	2012-07-10 06:59:08.328635216 +0300
+++ cc10.txt	2012-07-10 06:58:33.180646115 +0300
@@ -2,7 +2,7 @@
 btrfs: ffff8801cafbacc0: 00 00 63 72 06 01 00 00 00 80 00 00 00 00 00 00  ..cr............
 btrfs: ffff8801cafbacd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbace0: 35 00 00 00 00 00 00 00 30 00 d7 10 02 88 ff ff  5.......0.......
-btrfs: ffff8801cafbacf0: 23 23 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ##..............
+btrfs: ffff8801cafbacf0: 25 25 00 00 03 00 00 00 00 00 00 00 00 00 00 00  %%..............
 btrfs: ffff8801cafbad00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad20: 22 1c 00 00 00 00 00 00 00 00 00 00 00 00 00 00  "...............
--- cc10.txt	2012-07-10 06:58:33.180646115 +0300
+++ cc11.txt	2012-07-10 06:58:41.340643696 +0300
@@ -2,7 +2,7 @@
 btrfs: ffff8801cafbacc0: 00 00 63 72 06 01 00 00 00 80 00 00 00 00 00 00  ..cr............
 btrfs: ffff8801cafbacd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbace0: 35 00 00 00 00 00 00 00 30 00 d7 10 02 88 ff ff  5.......0.......
-btrfs: ffff8801cafbacf0: 25 25 00 00 03 00 00 00 00 00 00 00 00 00 00 00  %%..............
+btrfs: ffff8801cafbacf0: 27 27 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ''..............
 btrfs: ffff8801cafbad00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 btrfs: ffff8801cafbad20: 22 1c 00 00 00 00 00 00 00 00 00 00 00 00 00 00  "...............
------------------------------------------------------------

And since it's of course possible there's something wrong with my
modifications, here's the patch I used:

------------------------------------------------------------
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 7452ecb..aadb82c 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4527,6 +4527,9 @@ void read_extent_buffer(struct extent_buffer *eb, void *dstv,
 			len,
 			eb->debug[0], eb->debug[1], eb->debug[2], eb->debug[3],
 			eb->debug[4], eb->debug[5], eb->debug[6], eb->debug[7]);
+		printk(KERN_ERR "btrfs: --- start eb contents at %p ---\n", eb);
+		print_hex_dump(KERN_ERR, "btrfs: ", DUMP_PREFIX_ADDRESS, 16, 1, eb, sizeof(*eb), true);
+		printk(KERN_ERR "btrfs: --- end eb contents at %p ---\n", eb);
 		WARN_ON(1);
 	}
 	WARN_ON(start + len > eb->start + eb->len);
diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index ea81bd4..663d6c4 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -130,9 +130,13 @@ static int __readahead_hook(struct btrfs_root *root, struct extent_buffer *eb,
 		kref_get(&re->refcnt);
 	spin_unlock(&fs_info->reada_lock);
 
-	if (!err && btrfs_csum_tree_block(root, eb))
+	if (!err && btrfs_csum_tree_block(root, eb)) {
 		printk(KERN_ERR "btrfs: checksum mismatch 4 on %llu\n",
 			eb->start);
+		printk(KERN_ERR "btrfs: --- start eb contents at %p ---\n", eb);
+		print_hex_dump(KERN_ERR, "btrfs: ", DUMP_PREFIX_ADDRESS, 16, 1, eb, sizeof(*eb), true);
+		printk(KERN_ERR "btrfs: --- end eb contents at %p ---\n", eb);
+	}
 
 	if (!re)
 		return -1;
@@ -150,9 +154,14 @@ static int __readahead_hook(struct btrfs_root *root, struct extent_buffer *eb,
 	if (err == 0) {
 		nritems = level ? btrfs_header_nritems(eb) : 0;
 		if (level > BTRFS_MAX_LEVEL ||
-		    nritems > BTRFS_NODEPTRS_PER_BLOCK(root))
+		    nritems > BTRFS_NODEPTRS_PER_BLOCK(root)) {
 			printk(KERN_ERR "btrfs: node seems invalid now. checksum ok = %d\n",
 				btrfs_csum_tree_block(root, eb));
+			printk(KERN_ERR "btrfs: --- start eb contents at %p ---\n", eb);
+			print_hex_dump(KERN_ERR, "btrfs: ", DUMP_PREFIX_ADDRESS, 16, 1, eb, sizeof(*eb), true);
+			printk(KERN_ERR "btrfs: --- end eb contents at %p ---\n", eb);
+			
+		}
 		generation = btrfs_header_generation(eb);
 		/*
 		 * FIXME: currently we just set nritems to 0 if this is a leaf,
