[Ocfs2-devel] [PATCH] ocfs2: do not set OCFS2_LOCK_UPCONVERT_FINISHING if nonblocking lock can not be granted at once

[Xue jiufei]

Hi Junxiao

On 2014/11/7 13:54, Junxiao Bi wrote:
> Hi Jiufei,
> 
> On 11/07/2014 11:41 AM, Xue jiufei wrote:
>> Function ocfs2_readpages() use nonblocking flag to avoid page lock
>> inversion. It will trigger cluster hang because that flag
>> OCFS2_LOCK_UPCONVERT_FINISHING is not cleared if nonblocking lock
>> cannot be granted at once. The flag would prevent dc thread from
>> downconverting. So other nodes cannot acheive this lockres for ever.
>>
>> So we should not set OCFS2_LOCK_UPCONVERT_FINISHING when receiving ast
>> if nonblocking lock had already returned.
>>
> 
> Use OCFS2_LOCK_NONBLOCK_FINISHED can't fix this issue. Like there are
> two processes doing non-blocking lock in the following order.
I am wondering why these two processes can lock in such order.
> 1. Process A issue non-blocking lock fail, set OCFS2_LOCK_NONBLOCK_FINISHED.
We had set OCFS2_LOCK_BUSY flag before process A call ocfs2_dlm_lock(),
> 2. Process B issue non-blocking lock fail, set
> OCFS2_LOCK_NONBLOCK_FINISHED again.
So process B must wait until ast for Process A returns and clear OCFS2_LOCK_BUSY.

> 3. Ast for process A come, clear OCFS2_LOCK_NONBLOCK_FINISHED.
> 4. Ast for process B come, set OCFS2_LOCK_UPCONVERT_FINISHING.
> 
> So down convert can still be blocked.
> 
> To fix this issue, I think no need to call ocfs2_dlm_lock() for
> non-blocking lock, just check local lockres->l_level is enough, if
> request level equal or smaller than it, lock success, or lock fail.
> 
> Thanks,
> Junxiao.
> 
Thanks,
jiufei.

>> Signed-off-by: joyce.xue <xuejiufei at huawei.com>
>> ---
>>  fs/ocfs2/dlmglue.c | 37 +++++++++++++++++++++++++++++++------
>>  fs/ocfs2/ocfs2.h   |  6 ++++++
>>  2 files changed, 37 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
>> index 21262f2..1ddb6f1 100644
>> --- a/fs/ocfs2/dlmglue.c
>> +++ b/fs/ocfs2/dlmglue.c
>> @@ -861,8 +861,13 @@ static inline void ocfs2_generic_handle_convert_action(struct ocfs2_lock_res *lo
>>  	 * We set the OCFS2_LOCK_UPCONVERT_FINISHING flag before clearing
>>  	 * the OCFS2_LOCK_BUSY flag to prevent the dc thread from
>>  	 * downconverting the lock before the upconvert has fully completed.
>> +	 * Do not prevent the dc thread from downconverting if NONBLOCK lock
>> +	 * had already returned.
>>  	 */
>> -	lockres_or_flags(lockres, OCFS2_LOCK_UPCONVERT_FINISHING);
>> +	if (!(lockres->l_flags & OCFS2_LOCK_NONBLOCK_FINISHED))
>> +		lockres_or_flags(lockres, OCFS2_LOCK_UPCONVERT_FINISHING);
>> +	else
>> +		lockres_clear_flags(lockres, OCFS2_LOCK_NONBLOCK_FINISHED);
>>  
>>  	lockres_clear_flags(lockres, OCFS2_LOCK_BUSY);
>>  }
>> @@ -1324,13 +1329,12 @@ static void lockres_add_mask_waiter(struct ocfs2_lock_res *lockres,
>>  
>>  /* returns 0 if the mw that was removed was already satisfied, -EBUSY
>>   * if the mask still hadn't reached its goal */
>> -static int lockres_remove_mask_waiter(struct ocfs2_lock_res *lockres,
>> +static int __lockres_remove_mask_waiter(struct ocfs2_lock_res *lockres,
>>  				      struct ocfs2_mask_waiter *mw)
>>  {
>> -	unsigned long flags;
>>  	int ret = 0;
>>  
>> -	spin_lock_irqsave(&lockres->l_lock, flags);
>> +	assert_spin_locked(&lockres->l_lock);
>>  	if (!list_empty(&mw->mw_item)) {
>>  		if ((lockres->l_flags & mw->mw_mask) != mw->mw_goal)
>>  			ret = -EBUSY;
>> @@ -1338,6 +1342,18 @@ static int lockres_remove_mask_waiter(struct ocfs2_lock_res *lockres,
>>  		list_del_init(&mw->mw_item);
>>  		init_completion(&mw->mw_complete);
>>  	}
>> +
>> +	return ret;
>> +}
>> +
>> +static int lockres_remove_mask_waiter(struct ocfs2_lock_res *lockres,
>> +				      struct ocfs2_mask_waiter *mw)
>> +{
>> +	unsigned long flags;
>> +	int ret = 0;
>> +
>> +	spin_lock_irqsave(&lockres->l_lock, flags);
>> +	ret = __lockres_remove_mask_waiter(lockres, mw);
>>  	spin_unlock_irqrestore(&lockres->l_lock, flags);
>>  
>>  	return ret;
>> @@ -1373,6 +1389,7 @@ static int __ocfs2_cluster_lock(struct ocfs2_super *osb,
>>  	unsigned long flags;
>>  	unsigned int gen;
>>  	int noqueue_attempted = 0;
>> +	int dlm_locked = 0;
>>  
>>  	ocfs2_init_mask_waiter(&mw);
>>  
>> @@ -1481,6 +1498,7 @@ again:
>>  			ocfs2_recover_from_dlm_error(lockres, 1);
>>  			goto out;
>>  		}
>> +		dlm_locked = 1;
>>  
>>  		mlog(0, "lock %s, successful return from ocfs2_dlm_lock\n",
>>  		     lockres->l_name);
>> @@ -1514,10 +1532,17 @@ out:
>>  	if (wait && arg_flags & OCFS2_LOCK_NONBLOCK &&
>>  	    mw.mw_mask & (OCFS2_LOCK_BUSY|OCFS2_LOCK_BLOCKED)) {
>>  		wait = 0;
>> -		if (lockres_remove_mask_waiter(lockres, &mw))
>> +		spin_lock_irqsave(&lockres->l_lock, flags);
>> +		if (__lockres_remove_mask_waiter(lockres, &mw)) {
>> +			if (dlm_locked)
>> +				lockres_or_flags(lockres,
>> +					OCFS2_LOCK_NONBLOCK_FINISHED);
>> +			spin_unlock_irqrestore(&lockres->l_lock, flags);
>>  			ret = -EAGAIN;
>> -		else
>> +		} else {
>> +			spin_unlock_irqrestore(&lockres->l_lock, flags);
>>  			goto again;
>> +		}
>>  	}
>>  	if (wait) {
>>  		ret = ocfs2_wait_for_mask(&mw);
>> diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h
>> index bbec539..7d6b7d0 100644
>> --- a/fs/ocfs2/ocfs2.h
>> +++ b/fs/ocfs2/ocfs2.h
>> @@ -144,6 +144,12 @@ enum ocfs2_unlock_action {
>>  						     * before the upconvert
>>  						     * has completed */
>>  
>> +#define OCFS2_LOCK_NONBLOCK_FINISHED (0x00001000) /* NONBLOCK cluster
>> +						   * lock has already
>> +						   * returned, do not block
>> +						   * dc thread from
>> +						   * downconverting */
>> +
>>  struct ocfs2_lock_res_ops;
>>  
>>  typedef void (*ocfs2_lock_callback)(int status, unsigned long data);
>>
> 
> .
>