[mythtv] mythbackend 29/fixes crashes

[Ken Bass]

On 06/09/2018 06:58 AM, John Pilkington wrote:
> On 11/05/18 19:26, Ken Bass wrote:
>> 2 years ago I had reported frequent backend crashing in 0.28/fixes. 
>> We thought maybe it was due to an older Qt 5.6 in Centos 7.
>>
>> This past week I upgraded to the recently released Centos 7.5 which 
>> now includes Qt 5.9.2 and upgraded to v29.1-15-g280138b
>>
>> I am still experiencing crashing. They always seem to happen on an 
>> hour or 1/2 interval and seem to be related to QString()
>
> I didn't see anything that rang a bell in your examples, but I don't 
> have such crashes either.  I'm running master ad809c (Apr 10 rebuilt 
> May 14) on an el7.5 system (SL7.5 with elrepo 4.4.136 kernel, used 
> because it supports dvb adapter numbers).
>
> There can be build difficulties after subversion updates of el7, when 
> epel tracks el7 but the clones lag behind.
>
> Master has a recent commit for the SystemEventHandler  0c7ad11
Most of the crashes seem to be in QString--the segfaults would imply to 
me that there are string operations on NULL pointers going on.

For example many of the crashes in QString:append show it crashes on the 
following line:

(gdb) up
#4  0x00007fdff34f29c4 in MythSocket::WriteStringListReal 
(this=0x1cc64f0, list=0x7fdef4ff7ad0, ret=0x7fdef4ff75af) at 
mythsocket.cpp:727
727        QString str = list->join("[]:[]");

(gdb) p *list
$3 = {<QList<QString>> = {<QListSpecialMethods<QString>> = {<No data 
fields>}, {p = {static shared_null = {ref = {atomic = {
               _q_value = {<std::__atomic_base<int>> = {_M_i = -1}, <No 
data fields>}}}, alloc = 0, begin = 0, end = 0, array = {0x0}},
         d = 0x7fdedc048f30}, d = 0x7fdedc048f30}}, <No data fields>}

When it happens it is always the hour or 1/2 hour. I am not sure what 
happens at time but I am pretty sure it happens while live TV is playing 
somewhere. I don't think it I have seen it happen when idle or just 
recording things.