[Ocfs2-devel] [PATCH] Revert "ocfs2: mount shared volume without ha stack"

[heming.zhao at suse.com]

Hello Junxiao,

On 6/4/22 06:28, Junxiao Bi via Ocfs2-devel wrote:
> This reverts commit 912f655d78c5d4ad05eac287f23a435924df7144.
> 
> This commit introduced a regression that can cause mount hung.
> The changes in __ocfs2_find_empty_slot causes that any node with
> none-zero node number can grab the slot that was already taken by
> node 0, so node 1 will access the same journal with node 0, when it
> try to grab journal cluster lock, it will hung because it was already
> acquired by node 0.
> It's very easy to reproduce this, in one cluster, mount node 0 first,
> then node 1, you will see the following call trace from node 1.

 From your description, it looks your env mixed local-mount & clustered-mount.

Could you mind to share your test/reproducible steps.
And which ha stack do you use, pmck or o2cb?

I failed to reproduce it, my test steps (with pcmk stack):
```
node1:
mount -t ocfs2 /dev/vdd /mnt

node2:
for i in {1..100}; do
  echo "mount <$i>"; mount -t ocfs2 /dev/vdd /mnt;
  sleep 3;
  echo "umount"; umount /mnt;
done
```

This local mount feature helps SUSE customers to maintain ocfs2 partition, it's useful.
I want to find whether there is a idear way to fix the hung issue.

> 
> [13148.735424] INFO: task mount.ocfs2:53045 blocked for more than 122 seconds.
> [13148.739691]       Not tainted 5.15.0-2148.0.4.el8uek.mountracev2.x86_64 #2
> [13148.742560] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [13148.745846] task:mount.ocfs2     state:D stack:    0 pid:53045 ppid: 53044 flags:0x00004000
> [13148.749354] Call Trace:
> [13148.750718]  <TASK>
> [13148.752019]  ? usleep_range+0x90/0x89
> [13148.753882]  __schedule+0x210/0x567
> [13148.755684]  schedule+0x44/0xa8
> [13148.757270]  schedule_timeout+0x106/0x13c
> [13148.759273]  ? __prepare_to_swait+0x53/0x78
> [13148.761218]  __wait_for_common+0xae/0x163
> [13148.763144]  __ocfs2_cluster_lock.constprop.0+0x1d6/0x870 [ocfs2]
> [13148.765780]  ? ocfs2_inode_lock_full_nested+0x18d/0x398 [ocfs2]
> [13148.768312]  ocfs2_inode_lock_full_nested+0x18d/0x398 [ocfs2]
> [13148.770968]  ocfs2_journal_init+0x91/0x340 [ocfs2]
> [13148.773202]  ocfs2_check_volume+0x39/0x461 [ocfs2]
> [13148.775401]  ? iput+0x69/0xba
> [13148.777047]  ocfs2_mount_volume.isra.0.cold+0x40/0x1f5 [ocfs2]
> [13148.779646]  ocfs2_fill_super+0x54b/0x853 [ocfs2]
> [13148.781756]  mount_bdev+0x190/0x1b7
> [13148.783443]  ? ocfs2_remount+0x440/0x440 [ocfs2]
> [13148.785634]  legacy_get_tree+0x27/0x48
> [13148.787466]  vfs_get_tree+0x25/0xd0
> [13148.789270]  do_new_mount+0x18c/0x2d9
> [13148.791046]  __x64_sys_mount+0x10e/0x142
> [13148.792911]  do_syscall_64+0x3b/0x89
> [13148.794667]  entry_SYSCALL_64_after_hwframe+0x170/0x0
> [13148.797051] RIP: 0033:0x7f2309f6e26e
> [13148.798784] RSP: 002b:00007ffdcee7d408 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> [13148.801974] RAX: ffffffffffffffda RBX: 00007ffdcee7d4a0 RCX: 00007f2309f6e26e
> [13148.804815] RDX: 0000559aa762a8ae RSI: 0000559aa939d340 RDI: 0000559aa93a22b0
> [13148.807719] RBP: 00007ffdcee7d5b0 R08: 0000559aa93a2290 R09: 00007f230a0b4820
> [13148.810659] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffdcee7d420
> [13148.813609] R13: 0000000000000000 R14: 0000559aa939f000 R15: 0000000000000000
> [13148.816564]  </TASK>
> 
> To fix it, we can just fix __ocfs2_find_empty_slot. But original commit
> introduced the feature to mount ocfs2 locally even it is cluster based,
> that is a very dangerous, it can easily cause serious data corruption,
> there is no way to stop other nodes mounting the fs and corrupting it.

I can't follow your meaning. When users want to use local mount feature, they MUST know
what they are doing, and how to use it.

 From mount.ocfs2 (8), there also writes *only* mount fs on *one* node at the same time.
And also tell user fs will be damaged under wrong action.

```
nocluster

   This  option  allows  users  to  mount a clustered volume without configuring the cluster

   stack.  However, you must be aware that you can only mount the file system from one  node

   at the same time, otherwise, the file system may be damaged. Please use it with caution.
```

> Setup ha or other cluster-aware stack is just the cost that we have to
> take for avoiding corruption, otherwise we have to do it in kernel.

It's a little bit serious to totally revert this commit just under lacking sanity
check. If you or maintainer think the local mount should do more jobs to prevent mix
local-mount and clustered-mount scenario, we could add more sanity check during
local mounting.

Thanks,
Heming