[PATCH] btrfs: fix warning while merging two adjacent extents

[PATCH] btrfs: fix warning while merging two adjacent extents

[Gui Hecheng]

When we have two adjacent extents in relink_extent_backref,
we try to merge them. When we use btrfs_search_slot to locate the
slot for the current extent, we shouldn't set "ins_len = 1",
because we will merge it into the previous extent rather than
insert a new item. Otherwise, we may happen to create a new leaf
in btrfs_search_slot and path->slot[0] will be 0. Then we try to
fetch the previous item using "path->slots[0]--", and it will cause
a warning as follows:

	[  145.713385] WARNING: CPU: 3 PID: 1796 at fs/btrfs/extent_io.c:5043 map_private_extent_buffer+0xd4/0xe0
	[  145.713387] btrfs bad mapping eb start 5337088 len 4096, wanted 167772306 8
	...
	[  145.713462]  [<ffffffffa034b1f4>] map_private_extent_buffer+0xd4/0xe0
	[  145.713476]  [<ffffffffa030097a>] ? btrfs_free_path+0x2a/0x40
	[  145.713485]  [<ffffffffa0340864>] btrfs_get_token_64+0x64/0xf0
	[  145.713498]  [<ffffffffa033472c>] relink_extent_backref+0x41c/0x820
	[  145.713508]  [<ffffffffa0334d69>] btrfs_finish_ordered_io+0x239/0xa80

I encounter this warning when running defrag having mkfs.btrfs
with option -M. At the same time there are read/writes & snapshots
running at background.

Signed-off-by: Gui Hecheng <guihc.fnst@cn.fujitsu.com>
---
 fs/btrfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 1ea19ce..7f955d6 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2314,7 +2314,7 @@ again:
 		u64 extent_len;
 		struct btrfs_key found_key;
 
-		ret = btrfs_search_slot(trans, root, &key, path, 1, 1);
+		ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
 		if (ret < 0)
 			goto out_free_path;
 
-- 
1.8.0.1

Re: [PATCH] btrfs: fix warning while merging two adjacent extents

[Liu Bo]

On Thu, Jan 23, 2014 at 01:41:09PM +0800, Gui Hecheng wrote:
> When we have two adjacent extents in relink_extent_backref,
> we try to merge them. When we use btrfs_search_slot to locate the
> slot for the current extent, we shouldn't set "ins_len = 1",
> because we will merge it into the previous extent rather than
> insert a new item. Otherwise, we may happen to create a new leaf
> in btrfs_search_slot and path->slot[0] will be 0. Then we try to
> fetch the previous item using "path->slots[0]--", and it will cause
> a warning as follows:
> 
> 	[  145.713385] WARNING: CPU: 3 PID: 1796 at fs/btrfs/extent_io.c:5043 map_private_extent_buffer+0xd4/0xe0
> 	[  145.713387] btrfs bad mapping eb start 5337088 len 4096, wanted 167772306 8
> 	...
> 	[  145.713462]  [<ffffffffa034b1f4>] map_private_extent_buffer+0xd4/0xe0
> 	[  145.713476]  [<ffffffffa030097a>] ? btrfs_free_path+0x2a/0x40
> 	[  145.713485]  [<ffffffffa0340864>] btrfs_get_token_64+0x64/0xf0
> 	[  145.713498]  [<ffffffffa033472c>] relink_extent_backref+0x41c/0x820
> 	[  145.713508]  [<ffffffffa0334d69>] btrfs_finish_ordered_io+0x239/0xa80
> 
> I encounter this warning when running defrag having mkfs.btrfs
> with option -M. At the same time there are read/writes & snapshots
> running at background.

Looks good.

Reviewed-by: Liu Bo <bo.li.liu@oracle.com>

> 
> Signed-off-by: Gui Hecheng <guihc.fnst@cn.fujitsu.com>
> ---
>  fs/btrfs/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 1ea19ce..7f955d6 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -2314,7 +2314,7 @@ again:
>  		u64 extent_len;
>  		struct btrfs_key found_key;
>  
> -		ret = btrfs_search_slot(trans, root, &key, path, 1, 1);
> +		ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
>  		if (ret < 0)
>  			goto out_free_path;
>  
> -- 
> 1.8.0.1
> 
> --
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