Bug 895727

Summary: btrfs quotas are easy to get into an inconsistent state
Product: [Fedora] Fedora Reporter: Eric Hopper <eric-bugs2>
Component: kernelAssignee: Josef Bacik <josef>
Status: CLOSED UPSTREAM QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 18CC: gansalmon, itamar, jonathan, josef, kernel-maint, madhu.chinakonda, mmahut, zab
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Fixed In Version: Doc Type: Bug Fix
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Last Closed: 2013-09-23 20:28:40 UTC Type: Bug
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Flags
allow mounting of btrfs volumes with inconsistent quota information none

Description Eric Hopper 2013-01-15 21:19:25 UTC 
Description of problem:
Using a few commands related to btrfs quotas it's trivial to get btrfs into an inconsistent state

Version-Release number of selected component (if applicable):
Not sure exactly. The kernel shipped with Fedora 18 has the problem, but I'm not sure about kernels after that. I think they all do.

How reproducible:
Every time

Steps to Reproduce:
mkfs.btrfs /dev/sdb
mkdir /tmp/mnt
mount /dev/sdb /tmp/mnt
cd /tmp/mnt
btrfs quota enable .
btrfs subvol create foo
btrfs qgroup create 1/0
btrfs qgroup assign 0/257 1/0
btrfs subvol snapshot foo bar
btrfs qgroup assign 0/258 1/0
cd ..
umount /dev/sdb
mount /dev/sdb /tmp/mnt
# Still mountable!
cd mnt
btrfs qgroup destroy 1/0
cd ..
umount /dev/sdb
mount /dev/sdb /tmp/mnt
# Oops, no longer mountable, even in recovery mode!
  
Actual results:
Unmountable filesystem

Expected results:
A filesystem that I can still mount

Additional info:
http://www.spinics.net/lists/linux-btrfs/index.html#21463
Comment 1 Eric Hopper 2013-01-15 23:28:00 UTC 
This will likely need two fixes.

First, according to sensille (aka Arne Jansen, owner of this development tree http://git.kernel.org/?p=linux/kernel/git/arne/linux-btrfs.git;a=summary) on Freenode, inconsistencies in the quota subsystem are not supposed to prevent mounting.

Secondly, btrfs qgroup destroy leaves BTRFS_QGROUP_RELATION_KEY nodes lying around that refer to the destroyed qgroup. This should probably also be fixed.

I have a patch which I think should fix the first problem, and I will attach it to this bug.
Comment 2 Eric Hopper 2013-01-15 23:29:48 UTC 
Created attachment 679166 [details]
allow mounting of btrfs volumes with inconsistent quota information
Comment 3 Eric Hopper 2013-01-15 23:30:39 UTC 
This is a bug in btrfs, but at least part of it is within the kernel.
Comment 4 Eric Hopper 2013-01-16 06:05:19 UTC 
I verified my patch as working, though I'm not sure that it's the best possible patch, it is a patch that works.
Comment 5 Josh Boyer 2013-01-16 14:34:17 UTC 
(In reply to comment #4)
> I verified my patch as working, though I'm not sure that it's the best
> possible patch, it is a patch that works.

Did you send this to the upstream developers?
Comment 6 Eric Hopper 2013-01-16 15:22:50 UTC 
(In reply to comment #5)
> Did you send this to the upstream developers?

I sent the patch to the mailing list, yes.
Comment 7 Eric Hopper 2013-01-16 15:51:33 UTC 
http://www.spinics.net/lists/linux-btrfs/msg21464.html
Comment 8 Josef Bacik 2013-09-23 20:28:40 UTC 
Fixed upstream.