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
whatwe'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
wantto try to clean up our * transaction.  Just nail the windows shut and get out of town.  Now that * there's an
atexitcallback 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/PostgreSQL Development, 24x7 Support, Training &
Services