Re: 4.17-rc1 FS went read-only during balance

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

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On 2018年04月23日 13:08, Dmitrii Tcvetkov wrote:
> On Mon, 23 Apr 2018 09:23:53 +0800
> Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:
> 
>> On 2018年04月21日 22:55, Dmitrii Tcvetkov wrote:
>>> TL;DR It seems as regression in 4.17, but I managed to find a
>>> workaround to make filesystem rw mountable again.
>>>
>>> Kernel built from tag v4.17-rc1
>>> btrfs-progs 4.16
>>>
>>> Tonight two my machines (PC (ECC RAM) and laptop(non-ECC RAM)) were
>>> doing usual weekly balance with this command via cron:
>>> btrfs balance start -musage=50 -dusage=50 <mountpoint>
>>> Both machines run same kernel version. 
>>>
>>> On PC that caused root and "data" filesystems to go readonly. Root
>>> is on an SSD with data single and metadata DUP, "data" filesystem
>>> is on 2 HDDs with RAID1 for data and metadata.
>>>
>>> On laptop only /home went ro, it's on NVMe SSD with data single and
>>> metadata DUP. 
>>>
>>> Btrfs check of PC rootfs was without any errors in both modes, I did
>>> them once each before reboot on readonly filesystem with --force
>>> flag and then from live usb. Same output without any errors.
>>>
>>> After reboot kernel refused rw mount rootfs with the same error as
>>> during cron balance, ro mount was accepted, error during rw mount:
>>> BTRFS: error (device dm-17) in merge_reloc_roots:2465: errno=-117  
> 
>> 117 means EUCLEAN, which could be caused by the newly introduced
>> first_key and level check.
> 
>> Please apply this hotfix to fix it.
>> btrfs: Only check first key for committed tree blocks
>> (Which is included in latest pull request)
> 
>> Also, please consider enable CONFIG_BTRFS_DEBUG to provide extra
>> debug info.
> 
>> Thanks,
>> Qu
> 
> I tried 4.17-rc2 (as the pull request was pulled) with
> CONFIG_BTRFS_DEBUG on LVM snapshot of laptop home partition (/dev/vdb)
> in a VM (VM kernel sees only snapshot so no UUID collisions). Dmesg
> attached.

Thanks for the info and your previous btrfs-image.

The image itself shows nothing wrong, so it should be runtime problem.
Would you please apply these two debug patches?
https://patchwork.kernel.org/patch/10335133/
https://patchwork.kernel.org/patch/10335135/

And the attached diff file?

My guess is the parent node is not initialized correctly in this case.

Thanks,
Qu

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diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 60caa68c3618..79f482578e02 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -458,6 +458,7 @@ static int verify_level_key(struct btrfs_fs_info *fs_info,
 			  eb->start, first_key->objectid, first_key->type,
 			  first_key->offset, found_key.objectid,
 			  found_key.type, found_key.offset);
+		btrfs_print_tree(eb, false);
 	}
 #endif
 	return ret;
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 00b7d3231821..cde0cb6c9786 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1870,6 +1870,8 @@ int replace_path(struct btrfs_trans_handle *trans,
 					     level - 1, &first_key);
 			if (IS_ERR(eb)) {
 				ret = PTR_ERR(eb);
+				btrfs_err(fs_info, "parent leaf, slot: %d:", slot);
+				btrfs_print_tree(parent, false);
 				break;
 			} else if (!extent_buffer_uptodate(eb)) {
 				ret = -EIO;

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