Hi Junxiao,
Do you have any other questions about this solution?
On 2015/9/24 14:13, Joseph Qi wrote:
> On 2015/9/24 12:21, Junxiao Bi wrote:
>> On 09/24/2015 12:11 PM, Joseph Qi wrote:
>>> Hi Junxiao,
>>>
>>> On 2015/9/24 11:58, Junxiao Bi wrote:
>>>> On 09/24/2015 11:14 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 calls
>>>>> 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.
>>>> How this race windowed fixed?
>>>> the process have sent convert request to master node successfully(return
>>>> value DLM_NORMAL) then wait on LOCK_BUSY, then when master node panic
>>>> before send out ast, dlm_move_lockres_to_recovery_list() move the lock
>>>> to grant list. Ast never come.
>>> res->state is now having DLM_LOCK_RES_RECOVERING set.
>> But what happened if master node panic after
>> dlm_send_remote_convert_request() return DLM_NORMAL and wait on LOCK_BUSY?
>>
> Only two cases that it will call dlm_revert_pending_convert:
> 1) request returns other than DLM_NORMAL, current code will retry;
> 2) request returns DLM_NORMAL and recovery does it, this is the case we
> discuss. Consider the lockres spinlock has to be taken when doing this,
> only dlm_move_lockres_to_recovery_list runs first before request return
> code handling can we have the race window. If convert thread runs first,
> it's still in convert list, and recovery won't move it to grant list
> because convert_pending is cleared. And the new master will send ast
> after recovery.
>
> Thanks,
> Joseph
>
>> Thanks,
>> Junxiao.
>>
>> This patch will
>>> reset the status to DLM_RECOVERING and then retry convert request. Then
>>> new master will handle it and send ast.
>>>
>>>>
>>>> Thanks,
>>>> Junxiao.
>>>>
>>>>>
>>>>> 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, check if res->state has DLM_LOCK_RES_RECOVERING bit set
>>>>> (res is still in recovering) or res master changed (new master has
>>>>> finished recovery), reset the status to DLM_RECOVERING, then it will
>>>>> retry convert.
>>>>>
>>>>> Signed-off-by: Joseph Qi <joseph...@huawei.com>
>>>>> Reported-by: Yiwen Jiang <jiangyi...@huawei.com>
>>>>> Cc: <sta...@vger.kernel.org>
>>>>> ---
>>>>> fs/ocfs2/dlm/dlmconvert.c | 11 ++++++++++-
>>>>> 1 file changed, 10 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/fs/ocfs2/dlm/dlmconvert.c b/fs/ocfs2/dlm/dlmconvert.c
>>>>> index e36d63f..9e6116e 100644
>>>>> --- a/fs/ocfs2/dlm/dlmconvert.c
>>>>> +++ b/fs/ocfs2/dlm/dlmconvert.c
>>>>> @@ -262,6 +262,7 @@ enum dlm_status dlmconvert_remote(struct dlm_ctxt
>>>>> *dlm,
>>>>> struct dlm_lock *lock, int flags, int type)
>>>>> {
>>>>> enum dlm_status status;
>>>>> + u8 old_owner = res->owner;
>>>>>
>>>>> mlog(0, "type=%d, convert_type=%d, busy=%d\n", lock->ml.type,
>>>>> lock->ml.convert_type, res->state & DLM_LOCK_RES_IN_PROGRESS);
>>>>> @@ -316,11 +317,19 @@ enum dlm_status dlmconvert_remote(struct dlm_ctxt
>>>>> *dlm,
>>>>> spin_lock(&res->spinlock);
>>>>> res->state &= ~DLM_LOCK_RES_IN_PROGRESS;
>>>>> lock->convert_pending = 0;
>>>>> - /* if it failed, move it back to granted queue */
>>>>> + /* if it failed, move it back to granted queue.
>>>>> + * if master returns DLM_NORMAL and then down before sending ast,
>>>>> + * it may have already been moved to granted queue, reset to
>>>>> + * DLM_RECOVERING and retry convert */
>>>>> if (status != DLM_NORMAL) {
>>>>> if (status != DLM_NOTQUEUED)
>>>>> dlm_error(status);
>>>>> dlm_revert_pending_convert(res, lock);
>>>>> + } else if ((res->state & DLM_LOCK_RES_RECOVERING) ||
>>>>> + (old_owner != res->owner)) {
>>>>> + mlog(0, "res %.*s is in recovering or has been recovered.\n",
>>>>> + res->lockname.len, res->lockname.name);
>>>>> + status = DLM_RECOVERING;
>>>>> }
>>>>> bail:
>>>>> spin_unlock(&res->spinlock);
>>>>>
>>>>
>>>>
>>>> .
>>>>
>>>
>>>
>>
>>
>> .
>>
>
>
>
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