Re: [BUG] kernel BUG at fs/btrfs/async-thread.c:605!

From: Miao Xie <miaox@cn.fujitsu.com>
To: Eric Sandeen <sandeen@redhat.com>
Cc: Tsutomu Itoh <t-itoh@jp.fujitsu.com>,
	Linux Btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: [BUG] kernel BUG at fs/btrfs/async-thread.c:605!
Date: Mon, 04 Feb 2013 10:39:31 +0800	[thread overview]
Message-ID: <510F1F63.8000203@cn.fujitsu.com> (raw)
In-Reply-To: <510B5845.2020602@jp.fujitsu.com>

Hi, Eric

I want to send out my fix patch, but Could I add your Signed-off-by?
because you found the key to solving the problem.

Thanks
Miao

On Fri, 01 Feb 2013 14:53:09 +0900, Tsutomu Itoh wrote:
>>> Can you please explain similar problems, Miao?
>>
>> Before missing device check, there are several places where we read the metadata,
>> such as reading chunk tree root, btrfs_read_chunk_tree, those functions may fail
>> after submit a bio. If we don't wait until the bio end, and just stop the workers,
>> the same problem will happen.
>>
>> (invalidate_inode_pages2() will wait until the bio end, because it need lock the pages
>>   which are going to be invalidated, and the page is locked if it is under disk read IO)
> 
> I understood.
> 
> My reproducer is not reproduce this problem yet. But the following messages were
> displayed when 'rmmod btrfs' command was executed.
> 
>  [76378.723481] =============================================================================
>  [76378.723901] BUG btrfs_extent_buffer (Tainted: G   B       ): Objects remaining in btrfs_extent_buffer on kmem_cache_close()
>  [76378.724333] -----------------------------------------------------------------------------
>  [76378.724333]
>  [76378.724959] INFO: Slab 0xffffea00065c3280 objects=23 used=2 fp=0xffff8801970caac0 flags=0x8000000000004080
>  [76378.725391] Pid: 9156, comm: rmmod Tainted: G B        3.8.0-rc5 #1
>  [76378.725397] Call Trace:
>  [76378.725403]  [<ffffffff8111bc23>] slab_err+0xb0/0xd2
> 
> I think that this message means there is a possibility that I/O did not end
> normally.
> and, after Miao's patch applied, this message is not displayed when rmmod was
> executed.
> 
> So, Miao's patch seems to fix the problem for me.
[SNIP]
>>>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>>>> index 0c31d07..d8fd711 100644
>>>> --- a/fs/btrfs/disk-io.c
>>>> +++ b/fs/btrfs/disk-io.c
>>>> @@ -2728,13 +2728,13 @@ fail_cleaner:
>>>>    	 * kthreads
>>>>    	 */
>>>>    	filemap_write_and_wait(fs_info->btree_inode->i_mapping);
>>>> -	invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
>>>>    
>>>>    fail_block_groups:
>>>>    	btrfs_free_block_groups(fs_info);
>>>>    
>>>>    fail_tree_roots:
>>>>    	free_root_pointers(fs_info, 1);
>>>> +	invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
>>>>    
>>>>    fail_sb_buffer:
>>>>    	btrfs_stop_workers(&fs_info->generic_worker);
>>>> @@ -2755,7 +2755,6 @@ fail_alloc:
>>>>    fail_iput:
>>>>    	btrfs_mapping_tree_free(&fs_info->mapping_tree);
>>>>    
>>>> -	invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
>>>>    	iput(fs_info->btree_inode);
>>>>    fail_bdi:
>>>>    	bdi_destroy(&fs_info->bdi);
>>>>
> 
> 
> 