[Ocfs2-devel] [PATCH 1/1] ocfs2: fix ocfs2_find_slot repeats alloc same slot issue

[Junxiao Bi]

> 在 2022年6月13日，上午1:48，heming.zhao at suse.com 写道：
> 
> On 6/13/22 16:21, Joseph Qi wrote:
>>> On 6/13/22 3:59 PM, heming.zhao at suse.com wrote:
>>> On 6/12/22 22:16, Joseph Qi wrote:
>>>> Hi,
>>>> 
>>>> Why can't use local mount? I don't remember if we discuss about this.
>>>> 
>>> Sorry, I can't follow your question.
>>> Do you mean why revert commit 912f655d78c5?
>>> 
>>> or you are interest with the feature local mount?
>>> the local mount is created by mkfs.ocfs2, which can't be converted to clustered.
>>> see mkfs.ocfs2(8) '-M' option.
>>> 
>> What Junxiao's main concern is data corruption, so I'm afraid we have to
>> introduce an ondisk feature bit to prevent mixed nocluster and cluster
>> mount, similar to local mount.
> 
> this patch defined two new variants/flags:
> #define OCFS2_SLOTMAP_CLUSTER   1
> #define OCFS2_SLOTMAP_NOCLUSTER 2
> 
> (I expect) Under OCFS2_SLOTMAP_CLUSTER, for clustered mount mode and for compatibility,
> anything doesn't need to be changed.
> 
> OCFS2_SLOTMAP_NOCLUSTER will introduce a new value for slotmap area.
> this new value only take effect after a successfully nocluster mount.
> (pls fix me), existed kernel/user space code don't do any special handle for
> noclustered mount mode in slotmap area. So the new value is also compatibility.
> 
> And the patch can also prevent mixed mount, the related code is in ocfs2_find_slot().
> code logic:
> - noclustered mount condition: slotmap is empty or already mounted with noclustered
> - clustered mount condition: slotmap is empty or already mounted with clustered.
> - all other conditions will be denied.
Finding slot required reading slot map and then  update slot map. It is not atomic , you can’t prevent mixed mount until you have a cluster lock.
> 
>> Another scenario is journal replay after crash.
> 
> this patch set a rule:
> If last mount didn't do umount, (eg: crash happened), the next mount MUST be same mount type.
> (please also check above lines of 'code logic'.)
> 
> In my view, this rule is enough to handle crash scenario.
> So my patch should be polished in somewhere, but it is workable.
> 
> Thanks,
> Heming