Re: unrecognized node type while displaying a Path due to dangling pointer

On Tue, Jul 11, 2023 at 2:58 PM Jeevan Chalke <
jeevan(dot)chalke(at)enterprisedb(dot)com> wrote:

>
>
> On Tue, Jul 11, 2023 at 1:19 PM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
> wrote:
>
>> On 2023-Jul-11, Jeevan Chalke wrote:
>>
>> > 4. However, 2nd path was already sorted and passed as is to the
>> add_path().
>> > 5. add_path() decides to reject this new path on some metrics. However,
>> in
>> > the end, it pfree() this passed in path. It seems wrong as its
>> references
>> > do present elsewhere. For example, in the first path's parent rels path
>> > list.
>> > 6. So, while displaying the parent's path, we end up with these
>> warnings.
>>
>> In other words, this is use-after-free, with add_path freeing the
>> passed-in Path pointer, but one particular case in which this Path is
>> still used afterwards.
>>
>> > I tried to get a fix for this but no luck so far.
>>
>> I proposed to add an add_path_extended() function that adds 'bool
>> free_input_path' argument, and pass it false in that one place in
>> create_ordered_paths.
>>
>
> Yeah, this can be a way.
>
> However, I am thinking the other way around now. What if we first added
> the unmodified input path as it is to the ordered_rel first?
>
> If we do so, then while adding the next path, add_path() may decide to
> remove the older one as the newer path is the best one. The remove_old
> logic in add_path() will free the path (unsorted one), and we end up with
> the same error.
>
> And if we conditionally remove that path (remove_old logic one), then we
> need to pass false in every add_path() call in create_ordered_paths().
>

Attached patch.

>
> Am I missing something?
>
> Thanks
>
>
>>
>> --
>> Álvaro Herrera 48°01'N 7°57'E —
>> https://www.EnterpriseDB.com/
>>
>
>
> --
> Jeevan Chalke
>
> *Senior Staff SDE, Database Architect, and ManagerProduct Development*
>
>
>
> edbpostgres.com
>

--
Jeevan Chalke

*Senior Staff SDE, Database Architect, and ManagerProduct Development*

edbpostgres.com