Re: Possible problem with shm_mq spin lock

Hi,

On 2014-10-26 08:52:42 +1100, Haribabu Kommi wrote:
> I am thinking of a possible problem with shm_mq structure spin lock.
> This is used for protecting the shm_mq structure.
>
> During the processing of any code under the spin lock, if the process
> receives SIGQUIT signal then it is leading to a dead lock situation.
>
> SIGQUIT->proc_exit->shm_mq_detach->try to acquire spin lock. The spin
> lock is already took by the process.
>
> It is very dificult to reproduce the problem as because the code under
> the lock is very minimal.
> Please let me know if I missed anything.

I think you missed the following bit in postgres.c:

/*
* quickdie() occurs when signalled SIGQUIT by the postmaster.
*
* Some backend has bought the farm,
* so we need to stop what we're doing and exit.
*/
void
quickdie(SIGNAL_ARGS)
{
...
/*
* We DO NOT want to run proc_exit() callbacks -- we're here because
* shared memory may be corrupted, so we don't want to try to clean up our
* transaction. Just nail the windows shut and get out of town. Now that
* there's an atexit callback to prevent third-party code from breaking
* things by calling exit() directly, we have to reset the callbacks
* explicitly to make this work as intended.
*/
on_exit_reset();
..

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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