[U-Boot] [PATCH] fs: btrfs: Fix tree traversal with btrfs_next_slot()

[Yevgeny Popovych]

Hi Marek,

No hurry from my side, please take your time!

I think that might be the case for every file that is > 32 MiB
but it definitely depends on filesystem layout (other files) and
maybe some options (my EXTENT_DATA describe blocks of 1MiB size)?
This also can happen to almost any file that is > 1 MiB given that
there are enough files + some luck.

Bottom line - create a 50MiB file and add 50 2 MiB files to the
filesystem. I would expect that to create necessary conditions.
After trying to read the file - check file checksum
(no guarantee that it will end up with an error).

You can inspect FS with dump-tree to check if EXTENT_DATA items of
this inode (large file) is split across the tree leaves.

Thanks!


On 10/01/2018 01:35 PM, Marek Behún wrote:
> I shall test this today or tomorrow, but have too many things on my
> head, sorry :(
> You saying that this will fix reading large files? I haven't
> encountered such an error yet, but can try creating a large enough
> file. How large should it be? 
> 
> On Mon, 1 Oct 2018 08:50:11 +0300
> Yevgeny Popovych <yevgenyp at pointgrab.com> wrote:
> 
>> Just a kindly reminder :)
>>
>> On 09/07/2018 12:59 PM, Yevgeny Popovych wrote:
>>> When traversing slots in a btree (via btrfs_path) with
>>> btrfs_next_slot(), we didn't correctly identify that the last slot
>>> in the leaf was reached and we should jump to the next leaf.
>>>
>>> This could lead to any kind of runtime errors or corruptions, like:
>>> * file data not being read at all, or is read partially
>>> * file is read but is corrupted
>>> * (any) metadata being corrupted or not read at all, etc
>>>
>>> The easiest way to reproduce this is to read a large enough file
>>> that its EXTENT_DATA items don't fit into a single leaf.
>>>
>>> Signed-off-by: Yevgeny Popovych <yevgenyp at pointgrab.com>
>>> Cc: Marek Behun <marek.behun at nic.cz>
>>> ---
>>>  fs/btrfs/ctree.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
>>> index 4da36a9..b44a47e 100644
>>> --- a/fs/btrfs/ctree.c
>>> +++ b/fs/btrfs/ctree.c
>>> @@ -270,7 +270,7 @@ int btrfs_next_slot(struct btrfs_path *p)
>>>  {
>>>  	struct btrfs_leaf *leaf = &p->nodes[0]->leaf;
>>>  
>>> -	if (p->slots[0] >= leaf->header.nritems)
>>> +	if (p->slots[0] + 1 >= leaf->header.nritems)
>>>  		return jump_leaf(p, 1);
>>>  
>>>  	p->slots[0]++;
>>>   
>>
> 

-- 
Sincerely,
Yevgeny Popovych