On 2015/9/18 12:26, Tariq Saeed wrote:
> On 09/17/2015 06:17 AM, Joseph Qi wrote:
>> There is a race window between dlmconvert_remote and
>> dlm_move_lockres_to_recovery_list, which will cause a lock with
>> OCFS2_LOCK_BUSY in grant list, thus system hangs.
>>
>> dlmconvert_remote
>> {
>> spin_lock(&res->spinlock);
>> list_move_tail(&lock->list, &res->converting);
>> lock->convert_pending = 1;
>> spin_unlock(&res->spinlock);
>>
>> status = dlm_send_remote_convert_request();
>> >>>>>> race window, master has queued ast and return DLM_NORMAL,
>> and then down before sending ast.
>> this node detects master down and call
>> dlm_move_lockres_to_recovery_list, which will revert the
>> lock to grant list.
>> Then OCFS2_LOCK_BUSY won't be cleared as new master won't
>> send ast any more because it thinks already be authorized.
>>
>> spin_lock(&res->spinlock);
>> lock->convert_pending = 0;
>> if (status != DLM_NORMAL)
>> dlm_revert_pending_convert(res, lock);
>> spin_unlock(&res->spinlock);
>> }
>>
>> In this case, just leave it in convert list and new master will take
>> care of it after recovery. And if convert request returns other than
>> DLM_NORMAL, convert thread will do the revert itself.
>> So remove the revert logic in dlm_move_lockres_to_recovery_list.
>>
> First, I have a question about the old code you are removing.
> How did this scenario ever worked?
> convert req has been sent to the master and caller of __ocfs2_cluster_lock()
> is waiting in ocfs2_wait_for_mask(&mw) when master dies. new master
> receives the res with our lock in granted state (since we move it there
> in dlm_move_lockres_to_recovery_list). Now, the new master has no idea
> that this lock needs upconversion. How will it get converted?
As you can see, dlm_shuffle_lists won't handle this kind of lock.
That means the convert won't be finished forever.
>
> Now, back to your fix.This is my understanding.
> If we leave it in the converting list as you propose, then
> new master will also have it in converting list , its correct place.
>
> dlm_shuffle_lists runs after recovery. Will send BAST to the new master which
> would behave just like the original master would have. If lock can be
> converted,
> it will send AST, otherwise it will wait until it can be, just like the old
> master would
> have done etc etc. Am I correct?
Yes.
> Thanks
> -Tariq
>
> .
>
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