[Ocfs2-devel] [PATCH 1/2 v3] ocfs2/dlm: fix race between convert and recovery

[Joseph Qi]

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. 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.qi at huawei.com>
>> Reported-by: Yiwen Jiang <jiangyiwen at huawei.com>
>> Cc: <stable at 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);
>>
> 
> 
> .
>