Bug 1440051

+++ This bug was initially created as a clone of Bug #1439753 +++

+++ This bug was initially created as a clone of Bug #1434653 +++

Description of problem:
-----------------------
5 VM disk images are created on the fuse mounted sharded replica 3 volume of type 1x3. 5 VMs are installed, rebooted and are up. 3 more bricks are added to this volume to make it as 2x3. After performing rebalance, observed some wierd errors not allowing to login in to these VMs. When rebooted these VMs, they are unable to boot, which means that the VM disks are corrupted.

Version-Release number of selected component (if applicable):
-------------------------------------------------------------

glusterfs-3.8.10

How reproducible:
-----------------
Always

Steps to Reproduce:
-------------------
1. Create a sharded replica 3 volume
2. Optimize the volume for virt store usecase ( gluster volume set <vol> group virt ) and start the volume
3. Fuse mount the volume on another RHEL 7.3 Server ( used as hypervisor )
4. Create few disk images of size 10GB each
5. Start the VMs, install OS (RHEL 7.3) and reboot
6. When the VMs are up post installation, add 3 more bricks to the volume
7. Start rebalance process

Actual results:
---------------
VMs showed some errors on the console, which prevented from logging in. 
Post rebalance, when the VMs are rebooted, they are unable to boot with boot prompt showing up messages related to XFS inode corruption

Expected results:
-----------------
VM disks should not get corrupted.

--- Additional comment from SATHEESARAN on 2017-03-21 23:20:28 EDT ---

Setup Information
------------------


3. Volume info
--------------
# gluster volume info
 
Volume Name: trappist1
Type: Distributed-Replicate
Volume ID: 30e12835-0c21-4037-9f83-5556f3c637b6
Status: Started
Snapshot Count: 0
Number of Bricks: 2 x 3 = 6
Transport-type: tcp
Bricks:
Brick1: server1/gluster/brick1/b1
Brick2: server2:/gluster/brick1/b1
Brick3: server3:/gluster/brick1/b1
Brick4: server3::/gluster/brick2/b2 --> new brick added
Brick5: server1:/gluster/brick2/b2 --> new brick added
Brick6: server2:/gluster/brick2/b2 --> new brick added
Options Reconfigured:
network.ping-timeout: 30
performance.strict-o-direct: on
cluster.granular-entry-heal: enable
user.cifs: off
features.shard: on
cluster.shd-wait-qlength: 10000
cluster.shd-max-threads: 8
cluster.locking-scheme: granular
cluster.data-self-heal-algorithm: full
cluster.server-quorum-type: server
cluster.quorum-type: auto
cluster.eager-lock: enable
network.remote-dio: off
performance.low-prio-threads: 32
performance.stat-prefetch: off
performance.io-cache: off
performance.read-ahead: off
performance.quick-read: off
transport.address-family: inet
performance.readdir-ahead: on
nfs.disable: on

4. sharding related info
-------------------------
sharding is enabled on this volume with shard-block-size set to 4MB ( which is default )
[ granular-entry-heal enabled ]

5. Hypervisor details
----------------------
Host: rhs-client15.lab.eng.blr.redhat.com
mountpoint: /mnt/repvol

6.Virtual machine details
--------------------------
There are 4 virtual machines running in this host namely vm1,vm2,vm3,vm4,vm5 with their disk images on the fuse mounted gluster volume

[root@rhs-client15 ~]# virsh list --all
 Id    Name                           State
----------------------------------------------------
 6     vm1                            running
 7     vm2                            running
 8     vm3                            running
 9     vm4                            running
 10    vm5                            running


I have tested again with all the application VMs powered off. All VMs could boot healthy. The following are the test steps :

1. Create a sharded replica 3 volume and optimized the volume for virt store usecase
2. Created 5 VM image files on the fuse mounted gluster volume
3. Created 5 Application VMs with the above created VM images and installed OS ( RHEL7.3 ). Rebooted the VMs post OS installation.
4. Checked the health of all the VMs ( all VMs are healthy )
5. Powered off all the application VMs
6. Added 3 more bricks to convert 1x3 replicate volume to 2x3 distribute-replicate volume 
7. Initiated rebalance
8. Post rebalance has completed, started all the VMs. ( All VMs booted up healthy ) 

So, its the running VMs that are getting affected because of rebalance operation.

--- Additional comment from Raghavendra G on 2017-03-26 21:27:18 EDT ---

Conversation over mail:

> ​Raghu,
>
> In one of my test iteration, fix-layout itself caused corruption with VM
> disk.
> It happened only once, when I tried twice after that it never happened

One test is good enough to prove that we are dealing with at least one corruption issue, that is not the same as bz 1376757.

We need more analysis to figure out RCA.

>
> Thanks,
> Satheesaran S ( sas )​

--- Additional comment from SATHEESARAN on 2017-03-27 04:12:12 EDT ---

I have ran the test with the following combinations:
- Turning off strict-o-direct, and enabling remote-dio
I could still observe that VM disks are getting corrupted.

Also I did another test with sharding turned off, this issue was not seen.

--- Additional comment from Nithya Balachandran on 2017-03-29 23:28:52 EDT ---

Hi,

Is the system on which the issue was hit still available?

Thanks,
Nithya

--- Additional comment from Raghavendra G on 2017-04-01 00:52:31 EDT ---

Following is a rough algorithm of shard_writev:

1. Based on the offset, calculate the shards touched by current write.
2. Look for inodes corresponding to these shard files in itable.
3. If one or more inodes are missing from itable, issue mknod for corresponding shard files and ignore EEXIST in cbk.
4. resume writes on respective shards.

Now, imagine a write which falls to an existing "shard_file". For the sake of discussion lets consider a distribute of three subvols - s1, s2, s3

1. "shard_file" hashes to subvolume s2 and is present on s2
2. add a subvolume s4 and initiate a fix layout. The layout of ".shard" is fixed to include s4 and hash ranges are changed.
3. write that touches "shard_file" is issued.
4. The inode for "shard_file" is not present in itable after a graph switch and features/shard issues an mknod.
5. With new layout of .shard, lets say "shard_file" hashes to s3 and mknod (shard_file) on s3 succeeds. But, the shard_file is already present on s2.

So, we have two files on two different subvols of dht representing same shard and this will lead to corruption.

To prove the above hypothesis we need to look for one or more files (say "shard_file") in .shard present in more than one subvolume of dht. IOW, more than one subvolume of dht should have the file "/.shard/shard_file".

@Sas,

Is the setup still available? If yes, can you please take a look? Or if you can give me login details, I'll take a look. If the setup is not available, can you recreate the issue one more time so that I can take a look?

regards,
Raghavendra

--- Additional comment from Krutika Dhananjay on 2017-04-03 04:13:44 EDT ---

Whatever Raghavendra suspected in comment #12 is what we observed on sas' setup just now.

Following are the duplicate shards that exist on both subvolumes of DHT:

[root@dhcp37-65 tmp]# cat /tmp/shards-replicate-1 | sort | uniq -c | grep -v "1 "              
      2 702cd056-84d5-4c83-9232-cca363f2b3a7.1397
      2 702cd056-84d5-4c83-9232-cca363f2b3a7.1864
      2 702cd056-84d5-4c83-9232-cca363f2b3a7.487
      2 702cd056-84d5-4c83-9232-cca363f2b3a7.552
      2 702cd056-84d5-4c83-9232-cca363f2b3a7.7
      2 7a56bb45-91a0-49f4-a983-a8a46c418e04.487
      2 7a56bb45-91a0-49f4-a983-a8a46c418e04.509
      2 7a56bb45-91a0-49f4-a983-a8a46c418e04.521
      2 7a56bb45-91a0-49f4-a983-a8a46c418e04.7
      2 a37ab9d5-2f18-4916-9315-52476bd7ff54.1397
      2 a37ab9d5-2f18-4916-9315-52476bd7ff54.1398
      2 a37ab9d5-2f18-4916-9315-52476bd7ff54.576
      2 a37ab9d5-2f18-4916-9315-52476bd7ff54.7
      2 deaddfc9-f95e-4c26-9d4b-82d96e95057a.1397
      2 deaddfc9-f95e-4c26-9d4b-82d96e95057a.1398
      2 deaddfc9-f95e-4c26-9d4b-82d96e95057a.1867
      2 deaddfc9-f95e-4c26-9d4b-82d96e95057a.1868
      2 deaddfc9-f95e-4c26-9d4b-82d96e95057a.2
      2 deaddfc9-f95e-4c26-9d4b-82d96e95057a.487
      2 deaddfc9-f95e-4c26-9d4b-82d96e95057a.552
      2 deaddfc9-f95e-4c26-9d4b-82d96e95057a.576
      2 deaddfc9-f95e-4c26-9d4b-82d96e95057a.941
      2 ede69d31-f048-41b7-9173-448c7046d537.1397
      2 ede69d31-f048-41b7-9173-448c7046d537.1398
      2 ede69d31-f048-41b7-9173-448c7046d537.487
      2 ede69d31-f048-41b7-9173-448c7046d537.552
      2 ede69d31-f048-41b7-9173-448c7046d537.576
      2 ede69d31-f048-41b7-9173-448c7046d537.7

Worse yet, the md5sums of the two copies differ.

For instance,

On replicate-0:
[root@dhcp37-65 tmp]# md5sum /gluster/brick1/b1/.shard/702cd056-84d5-4c83-9232-cca363f2b3a7.1397
1e86d0a097c724965413d07af71c0809  /gluster/brick1/b1/.shard/702cd056-84d5-4c83-9232-cca363f2b3a7.1397

On replicate-1:
[root@dhcp37-85 tmp]# md5sum /gluster/brick2/b2/.shard/702cd056-84d5-4c83-9232-cca363f2b3a7.1397
e72cc949c7ba9b76d350a77be932ba3f  /gluster/brick2/b2/.shard/702cd056-84d5-4c83-9232-cca363f2b3a7.1397

Raghavendra will be sending out a fix in DHT for this issue.

--- Additional comment from SATHEESARAN on 2017-04-03 04:23:01 EDT ---

(In reply to Raghavendra G from comment #12)

> @Sas,
> 
> Is the setup still available? If yes, can you please take a look? Or if you
> can give me login details, I'll take a look. If the setup is not available,
> can you recreate the issue one more time so that I can take a look?
> 
> regards,
> Raghavendra

I have already shared the setup details in the mail.
Let me know, if you need anything more

--- Additional comment from Raghavendra G on 2017-04-04 00:44:56 EDT ---

The fix itself is fairly simple:

In all entry fops - create, mknod, symlink, open with O_CREATE, link, rename, mkdir etc, we have to do:

Check volume commit hash is equal to the commit hash on parent inode
1. If yes, proceed with the dentry fop
2. else, 
   a. initiate a lookup(frame, this, loc). IOW, Wind the lookup on the location structure passed as an arg to DHT (not directly to its subvols)
   b. Once all lookups initiated in "a." are complete, resume the dentry fop.

For the scope of this bug its sufficient to fix dht_mknod. But, for completeness sake (and to avoid similar bugs in other codepaths [2]) I would prefer to fix all codepaths. So, the codepaths affected are more and hence more testing.

[1] is another VM corruption issue during rebalance.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1276062
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1286127