Re: Segment fault when excuting SPI function On PG with commit 41c6a5be

Michael Paquier <michael@paquier.xyz>

From: Michael Paquier <michael@paquier.xyz>
To: "liuhuailing@fujitsu.com" <liuhuailing@fujitsu.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2021-07-30T12:38:01Z
Lists: pgsql-hackers
On Fri, Jul 30, 2021 at 08:57:35AM +0000, liuhuailing@fujitsu.com wrote:
> When I used SPI_execute_plan function on PG12 which commit 41c6a5be is used,
> Segment fault occurred.
> 
> PS: If commit 41c6a5be is not used, this phenomenon will not happen. 

I see nothing wrong in this commit, FWIW.

> Reproduce:
> In a background process, the following steps are executed.
> --------------------------
> StartTransactionCommand();
> SPI_connect();       
> plan = SPI_prepare(query,0,NULL); ★the query is a SELECT SQL. 
> SPI_keepplan(plan);         
> SPI_finish();           
> CommitTransactionCommand();   
> StartTransactionCommand();    
> SPI_connect();
> SPI_execute_plan(plan, NULL, NULL, true, 0); ★Segment fault
> --------------------------

But I see an issue with your code.  It seems to me that you should
push a snapshot before doing SPI_prepare() and SPI_execute_plan(),
as of:
PushActiveSnapshot(GetTransactionSnapshot()); 
--
Michael

Commits

  1. Use elog, not Assert, to report failure to provide an outer snapshot.

  2. Restore the portal-level snapshot after procedure COMMIT/ROLLBACK.