Re: [dpdk-dev] [PATCH 3/4] eal: don't crash if alarm set fails

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 18-Sep-18 10:43 AM, Thomas Monjalon wrote:
> 26/07/2018 11:41, Burakov, Anatoly:
>> On 25-Jul-18 7:20 PM, Stephen Hemminger wrote:
>>> There is no need to call rte_exit and crash the application here;
>>> better to let the application handle the error itself.
>>>
>>> Remove the gratuitous profanity which would be visible if
>>> the rte_exit was still there.
>>>
>>> Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
>>> ---
>>> --- a/lib/librte_eal/common/eal_common_proc.c
>>> +++ b/lib/librte_eal/common/eal_common_proc.c
>>> @@ -841,14 +841,12 @@ mp_request_async(const char *dst, struct rte_mp_msg *req,
>>>    
>>>    	param->user_reply.nb_sent++;
>>>    
>>> -	if (rte_eal_alarm_set(ts->tv_sec * 1000000 + ts->tv_nsec / 1000,
>>> -			      async_reply_handle, pending_req) < 0) {
>>> +	ret = rte_eal_alarm_set(ts->tv_sec * 1000000 + ts->tv_nsec / 1000,
>>> +				async_reply_handle, pending_req);
>>> +	if (ret < 0)
>>>    		RTE_LOG(ERR, EAL, "Fail to set alarm for request %s:%s\n",
>>>    			dst, req->name);
>>> -		rte_panic("Fix the above shit to properly free all memory\n");
>>
>> Profanity aside, i think the message was trying to tell me something -
>> namely, that if alarm_set fails, we're risking to leak this memory if
>> reply from the peer never comes, and we're risking leaving the
>> application hanging because the timeout never triggers. I'm not sure if
>> leaving this "to the user" is the right choice, because there is no way
>> for the user to free IPC-internal memory if it leaks.
>>
>> So i think the proper way to handle this would've been to set the alarm
>> first, then, if it fails, don't sent the message in the first place.
> 
> What should be done here? OK to remove rte_panic for now?
> 

As i said, the above fix is wrong because it leaks memory (however 
unlikely it may be).

The alarm set call should be moved to before we do send_msg() call (and 
goto fail; on failure). That way, even if alarm triggers too early (i.e. 
immediately), the requests tailq will still be locked until we complete 
our request sends - so we appropriately free memory on response, on 
timeout or in our failure handler if alarm set has failed.

-- 
Thanks,
Anatoly