Re: [PATCH] btrfs: Remove WARN_ON for unaligned device created before v4.13 and adds more user friendly output

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2017年09月23日 09:27, Satoru Takeuchi wrote:
> At Sat, 23 Sep 2017 10:19:26 +0900,
> Satoru Takeuchi wrote:
>>
>> At Wed, 20 Sep 2017 15:18:43 +0900,
>> Qu Wenruo wrote:
>>>
>>> Commit 7dfb8be11b5d ("btrfs: Round down values which are written for
>>> total_bytes_size") is fixing the unaligned device size caused by
>>> adding/shrinking device.
>>>
>>> It added a new WARN_ON() when device size is unaligned.
>>> This is fine for new device added to btrfs using v4.13 kernel, but not
>>> existing device whose total_bytes is already unaligned.
>>>
>>> And the WARN_ON() will get triggered every time a block group get
>>> created/removed on the unaligned device.
>>>
>>> This patch will remove the WARN_ON(), and warn user more gently what's
>>> happening and how to fix it.
>>>
>>> Reported-by: Rich Rauenzahn <rich@shroop.net>
>>> Fixes: 7dfb8be11b5d ("btrfs: Round down values which are written for
>>> total_bytes_size")
>>> Signed-off-by: Qu Wenruo <quwenruo.btrfs@gmx.com>
>>> ---
>>>   fs/btrfs/ctree.h   |  1 -
>>>   fs/btrfs/volumes.c | 16 ++++++++++++----
>>>   2 files changed, 12 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>>> index 5a8933da39a7..4de9269e435a 100644
>>> --- a/fs/btrfs/ctree.h
>>> +++ b/fs/btrfs/ctree.h
>>> @@ -1562,7 +1562,6 @@ static inline void btrfs_set_device_total_bytes(struct extent_buffer *eb,
>>>   {
>>>   	BUILD_BUG_ON(sizeof(u64) !=
>>>   		     sizeof(((struct btrfs_dev_item *)0))->total_bytes);
>>> -	WARN_ON(!IS_ALIGNED(val, eb->fs_info->sectorsize));
>>>   	btrfs_set_64(eb, s, offsetof(struct btrfs_dev_item, total_bytes), val);
>>>   }
>>>   
>>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>>> index 0e8f16c305df..afae25df6a8c 100644
>>> --- a/fs/btrfs/volumes.c
>>> +++ b/fs/btrfs/volumes.c
>>> @@ -6472,15 +6472,23 @@ static int read_one_chunk(struct btrfs_fs_info *fs_info, struct btrfs_key *key,
>>>   	return 0;
>>>   }
>>>   
>>> -static void fill_device_from_item(struct extent_buffer *leaf,
>>> -				 struct btrfs_dev_item *dev_item,
>>> -				 struct btrfs_device *device)
>>> +static void fill_device_from_item(struct btrfs_fs_info *fs_info,
>>> +				  struct extent_buffer *leaf,
>>> +				  struct btrfs_dev_item *dev_item,
>>> +				  struct btrfs_device *device)
>>>   {
>>>   	unsigned long ptr;
>>>   
>>>   	device->devid = btrfs_device_id(leaf, dev_item);
>>>   	device->disk_total_bytes = btrfs_device_total_bytes(leaf, dev_item);
>>>   	device->total_bytes = device->disk_total_bytes;
>>> +	if (!IS_ALIGNED(device->total_bytes, fs_info->sectorsize)) {
>>> +		btrfs_warn(fs_info,
>>> +			   "devid %llu has unaligned total bytes %llu",
>>> +			   device->devid, device->disk_total_bytes);
>>> +		btrfs_warn(fs_info,
>>> +			   "please shrink the device a little and resize back to fix it");
>>> +	}
>>
>> How about telling uses to know device->total_bytes should be alligned
>> to fs_info->sectorsize here?
>>
>> Thanks,
> 
> I should make my comment clearer, sorry.
> 
> ===
> +	if (!IS_ALIGNED(device->total_bytes, fs_info->sectorsize)) {
> +		btrfs_warn(fs_info,
> +			   "devid %llu: total bytes %llu should be aligned to %u bytes",
> +			   device->devid, device->disk_total_bytes, fs_info->sectorsize);
> +		btrfs_warn(fs_info,
> +			   "please shrink the device a little and resize back to fix it");
> +	}
> ===

That's better.

But I'm also considering modifying the total_bytes directly here.
So that any time DEV_ITEM and super block get updated, new aligned value 
will be written back to disk, and since the value is aligned in memory, 
it won't cause WARN_ON() any longer.

I'll test and check the code for confirmation before updating the patch.

Thanks,
Qu

> 
> Thanks,
> Satoru
> 
>> Satoru
>>
>>>   	device->commit_total_bytes = device->disk_total_bytes;
>>>   	device->bytes_used = btrfs_device_bytes_used(leaf, dev_item);
>>>   	device->commit_bytes_used = device->bytes_used;
>>> @@ -6625,7 +6633,7 @@ static int read_one_dev(struct btrfs_fs_info *fs_info,
>>>   			return -EINVAL;
>>>   	}
>>>   
>>> -	fill_device_from_item(leaf, dev_item, device);
>>> +	fill_device_from_item(fs_info, leaf, dev_item, device);
>>>   	device->in_fs_metadata = 1;
>>>   	if (device->writeable && !device->is_tgtdev_for_dev_replace) {
>>>   		device->fs_devices->total_rw_bytes += device->total_bytes;
>>> -- 
>>> 2.14.1
>>>
>>> --
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