[PATCH] btrfs: Fix scrub panic when leaf accross stripes

[PATCH] btrfs: Fix scrub panic when leaf accross stripes

[Zhaolei]

From: Zhao Lei <zhaolei@cn.fujitsu.com>

Scrub panic in following operation:
  mkfs.ext4 /dev/vdh
  btrfs-convert /dev/vdh
  mount /dev/vdh /mnt/tmp1
  btrfs scrub start -B /dev/vdh
  (panic)

Reason:
  1: In some case, leaf created by btrfs-convert was splited into 2
     strips.
  2: Scrub bypassed part of above wrong leaf data, but remain data
     caused panic in scrub_checksum_tree_block().

For reason 1:
  we can get following information after some simple operation.
  a. mkfs.ext4 /dev/vdh
     btrfs-convert /dev/vdh
  b. btrfs-debug-tree /dev/vdh
     we can see following item in extent tree:
     item 25 key (27054080 METADATA_ITEM 0) itemoff 15083 itemsize 33
     Its logical address is [27054080, 27070464)
     and acrossed 2 strips:
     [27000832, 27066368)
     [27066368, 27131904)
  Will be fixed in btrfs-progs(btrfs-convert, btrfsck, ...)

For reason 2:
  Scrub is trying to do a "bypass" in this case, but the result is
  "panic", because current code lacks of some condition in bypass,
  and let some wrong leaf data escaped.

This patch fixed above scrub code.

Before patch:
  # btrfs scrub start -B /dev/vdh
  (panic)

After patch:
  # btrfs scrub start -B /dev/vdh
  scrub done for 353cec8f-da31-4a94-aa35-be72d997b06e
  ...
  # dmesg
  ...
  [   59.088697] BTRFS error (device vdh): scrub: tree block 27054080 spanning stripes, ignored. logical=27000832
  [   59.089929] BTRFS error (device vdh): scrub: tree block 27054080 spanning stripes, ignored. logical=27066368
  #

Reported-by: Chris Murphy <lists@colorremedies.com>
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
---
 fs/btrfs/scrub.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 94db0fa..35d49b2 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -2881,11 +2881,12 @@ static noinline_for_stack int scrub_raid56_parity(struct scrub_ctx *sctx,
 			flags = btrfs_extent_flags(l, extent);
 			generation = btrfs_extent_generation(l, extent);
 
-			if (key.objectid < logic_start &&
-			    (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)) {
-				btrfs_err(fs_info,
-					  "scrub: tree block %llu spanning stripes, ignored. logical=%llu",
-					   key.objectid, logic_start);
+			if ((flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) &&
+			    (key.objectid < logic_start ||
+			     key.objectid + bytes >
+			     logic_start + map->stripe_len)) {
+				btrfs_err(fs_info, "scrub: tree block %llu spanning stripes, ignored. logical=%llu",
+					  key.objectid, logic_start);
 				goto next;
 			}
 again:
@@ -3212,8 +3213,10 @@ static noinline_for_stack int scrub_stripe(struct scrub_ctx *sctx,
 			flags = btrfs_extent_flags(l, extent);
 			generation = btrfs_extent_generation(l, extent);
 
-			if (key.objectid < logical &&
-			    (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)) {
+			if ((flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) &&
+			    (key.objectid < logical ||
+			     key.objectid + bytes >
+			     logical + map->stripe_len)) {
 				btrfs_err(fs_info,
 					   "scrub: tree block %llu spanning "
 					   "stripes, ignored. logical=%llu",
-- 
1.8.5.1

Re: [PATCH] btrfs: Fix scrub panic when leaf accross stripes

[Chris Mason]

On Thu, Jul 23, 2015 at 12:29:49PM +0800, Zhaolei wrote:
> From: Zhao Lei <zhaolei@cn.fujitsu.com>
> 
> Scrub panic in following operation:
>   mkfs.ext4 /dev/vdh
>   btrfs-convert /dev/vdh
>   mount /dev/vdh /mnt/tmp1
>   btrfs scrub start -B /dev/vdh
>   (panic)
> 
> Reason:
>   1: In some case, leaf created by btrfs-convert was splited into 2
>      strips.
>   2: Scrub bypassed part of above wrong leaf data, but remain data
>      caused panic in scrub_checksum_tree_block().

Thanks for tracking this one down, I've queued it up.

-chris