Ocfs2 devel - Jun 2022 - [PATCH] Revert "ocfs2: mount shared volume without ha stack"

On 6/5/22 7:08 PM, heming.zhao at suse.com wrote:
> Hello Junxiao,
>
> First of all, let's turn to the same channel to discuss your patch.
> There are two features: 'local mount' & 'nocluster
mount'.
> I mistakenly wrote local-mount on some place in previous mails.
> This patch revert commit 912f655d78c5d4, which is related with
'nocluster mount'.
>
>
> On 6/5/22 00:19, Junxiao Bi wrote:
>>
>>> ? 2022?6?4????1:45?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.
>> No, only cluster 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
>>> ```
>>>
>> Try set one node with node number 0 and mount it there first. I used
o2cb stack.
> Could you show more test info/steps. I can't follow your meaning.
> How to set up a node with a fix node number?
> With my understanding, under pcmk env, the first mounted node will auto got
node
> number 1 (or any value great than 0). and there is no place to set node
number
> by hand. It's very likely you mixed to use nocluster & cluster
mount.
> If my suspect right (mixed mount), your use case is wrong.
Did you check my last mail? I already said i didn't do mixed mount, only 
cluster mount.

There is a configure file for o2cb, you can just set node number to 0, 
please check 
https://docs.oracle.com/en/operating-systems/oracle-linux/7/fsadmin/ol7-ocfs2.html#ol7-config-file-ocfs2
>
>>> 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:
>>>> ...
>>>> 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.
>> I can?t agree with you. There is no  mechanism to make sure customer
will follow that, you can?t expect customer understand tech well or even read
the doc.
> yes, no one reads doc by default.
>
> currently, mount with option 'nocluster' will show special info to
user:
>
> ```
> # mount -t ocfs2 -o nocluster /dev/vdd /mnt
> Warning: to mount a clustered volume without the cluster stack.
> Please make sure you only mount the file system from one node.
> Otherwise, the file system may be damaged.
> Proceed (y/N):
> ```
>
>> It?s not the case that you don?t have choice, setup cluster stack is
the way to stop customer doing something bad, I believe you have to educate
customer to understand this is the cost to guard data security, otherwise when
something bad happens, they will lose important data, maybe even no way to
recover.
> This feature is not enabled by default, and also shows enough info/warn
before executing.
> I give (may awkward) another example:
> nocluster mount likes executing command 'rm -rf /', do you think we
should
> tell/educate customer do not execute it?
That's totally out of domain of ocfs2, it's not ocfs2 developer's
job to
tell customer not doing that.

Here you provided a ocfs2 feature that can easily corrupt ocfs2.

As an ocfs2 developer, you should make sure ocfs2 was not corrupted even 
customer did something bad. That's why mkfs.ocfs2/fsck.ocfs2 check 
whether ocfs2 volume is mounted in the cluster before changing anything.
>
> The nocluster mount feature was designed to resolve customer pain point
from real world:
> SUSE HA stack uses pacemaker+corosync+fsdlm+ocfs2, which
complicates/inconveniences
> to set up. and need to install dozens of related packages.
>
> The nocluster feature main use case:
> customer wants to avoid to set up HA stack, but they wants to check ocfs2
volume
> or do backup volume.
That doesn't mean you have to do this in kernel. Customer had a pain to 
setup HA stack, you should develop some script/app to make it
easy.
>
> In my opinion, we should make ocfs2 more powerful and include more useful
features for users.
> If there are some problems related new feature, we should do our best to
fix it not revert it.
Only good/safe features, i don't think this one is qualified. Also no 
one give a reviewed-by to this commit, i am not sure how it was merged.

Joseph, what's your call on this?

Thanks,

Junxiao.
>>>   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.
>> I don?t think this should be done in kernel. Setup cluster stack is the
way to forward.
>>
> my mistake: all above 'local mount' should be 'nocluster
mount'.
>
> At last, let's totally understand your use case (or reproduce your hung
issue).
>
> Thanks,
> Heming
>

On 6/7/22 00:15, Junxiao Bi wrote:
> On 6/5/22 7:08 PM, heming.zhao at suse.com wrote:
> 
>> Hello Junxiao,
>>
>> First of all, let's turn to the same channel to discuss your patch.
>> There are two features: 'local mount' & 'nocluster
mount'.
>> I mistakenly wrote local-mount on some place in previous mails.
>> This patch revert commit 912f655d78c5d4, which is related with
'nocluster mount'.
>>
>>
>> On 6/5/22 00:19, Junxiao Bi wrote:
>>>
>>>> ? 2022?6?4????1:45?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.
>>> No, only cluster 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
>>>> ```
>>>>
>>> Try set one node with node number 0 and mount it there first. I
used o2cb stack.
>> Could you show more test info/steps. I can't follow your meaning.
>> How to set up a node with a fix node number?
>> With my understanding, under pcmk env, the first mounted node will auto
got node
>> number 1 (or any value great than 0). and there is no place to set node
number
>> by hand. It's very likely you mixed to use nocluster & cluster
mount.
>> If my suspect right (mixed mount), your use case is wrong.
> 
> Did you check my last mail? I already said i didn't do mixed mount,
only cluster mount.
I carefully read every word of your mails. we are in different world. (pcmk vs
o2cb)
In pcmk env, slot number always great than 0. (I also maintain cluster-md in
suse,
in slot_number at drivers/md/md-cluster.c, you can see the number never ZERO).
> 
> There is a configure file for o2cb, you can just set node number to 0,
please check
https://docs.oracle.com/en/operating-systems/oracle-linux/7/fsadmin/ol7-ocfs2.html#ol7-config-file-ocfs2
Thank you for sharing. I will read & learn it.
> 
>>
>>>> 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:
>>>>> ...
>>>>> 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.
>>> I can?t agree with you. There is no? mechanism to make sure
customer will follow that, you can?t expect customer understand tech well or
even read the doc.
>> yes, no one reads doc by default.
>>
>> currently, mount with option 'nocluster' will show special info
to user:
>>
>> ```
>> # mount -t ocfs2 -o nocluster /dev/vdd /mnt
>> Warning: to mount a clustered volume without the cluster stack.
>> Please make sure you only mount the file system from one node.
>> Otherwise, the file system may be damaged.
>> Proceed (y/N):
>> ```
>>
>>> It?s not the case that you don?t have choice, setup cluster stack
is the way to stop customer doing something bad, I believe you have to educate
customer to understand this is the cost to guard data security, otherwise when
something bad happens, they will lose important data, maybe even no way to
recover.
>> This feature is not enabled by default, and also shows enough info/warn
before executing.
>> I give (may awkward) another example:
>> nocluster mount likes executing command 'rm -rf /', do you
think we should
>> tell/educate customer do not execute it?
> 
> That's totally out of domain of ocfs2, it's not ocfs2
developer's job to tell customer not doing that.
> 
> Here you provided a ocfs2 feature that can easily corrupt ocfs2.
First, this hung issue or any other related issues can be fixed. I have already
described a method in my previous mail. (use es_reserved1[0] of
ocfs2_extended_slot)

Second, this feature have been merged two years, only you reported a hung issue.
Our customer also uses it for 2 years, no bug reported from them. it means,
at least, this feature fine works in pcmk stack.
> 
> As an ocfs2 developer, you should make sure ocfs2 was not corrupted even
customer did something bad. That's why mkfs.ocfs2/fsck.ocfs2 check whether
ocfs2 volume is mounted in the cluster before changing anything.
fsck.ocfs2 with '-F' could work in noclustered env.
In 2005, commit 44c97d6ce8baeb4a6c37712d4c22d0702ebf7714 introduced this
feature.
This year, commit 7085e9177adc7197250d872c50a05dfc9c531bdc enhanced it,
which could make fsck.ocfs2 totally work in noclustered env.
(mkfs.ocfs2 can also work in local mount mode which is another story)
> 
>>
>> The nocluster mount feature was designed to resolve customer pain point
from real world:
>> SUSE HA stack uses pacemaker+corosync+fsdlm+ocfs2, which
complicates/inconveniences
>> to set up. and need to install dozens of related packages.
>>
>> The nocluster feature main use case:
>> customer wants to avoid to set up HA stack, but they wants to check
ocfs2 volume
>> or do backup volume.
> That doesn't mean you have to do this in kernel. Customer had a pain to
setup HA stack, you should develop some script/app to make it easy.
It's not a simple job to develop some script/app to help setup ha stack.
Both SUSE and Red Hat have special team to do this. In SUSE, this team have
worked many years.
If any one can create an easy/powerful HA auto setup tools, He can even found a
company
to sell this software.
>>
>> In my opinion, we should make ocfs2 more powerful and include more
useful features for users.
>> If there are some problems related new feature, we should do our best
to fix it not revert it.
> 
> Only good/safe features, i don't think this one is qualified. Also no
one give a reviewed-by to this commit, i am not sure how it was merged.
I had shared my idea about how to fix this hung issue. it's not a big bug.
More useful feature could attract more users, it will make ocfs2 community more
powerful.
> 
> Joseph, what's your call on this?
me too, wait for maintainer feedback.

/Heming
> 
> Thanks,
> 
> Junxiao.
> 
>>>> ? 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.
>>> I don?t think this should be done in kernel. Setup cluster stack is
the way to forward.
>>>
>> my mistake: all above 'local mount' should be 'nocluster
mount'.
>>
>> At last, let's totally understand your use case (or reproduce your
hung issue).
>>
>> Thanks,
>> Heming
>>
>