Re: possible dsm bug in dsm_attach()

On Tue, May 6, 2014 at 8:43 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> dsm_attach() does the following:
>
> nitems = dsm_control->nitems;
> for (i = 0; i < nitems; ++i)
> {
> /* If the reference count is 0, the slot is actually unused. */
> if (dsm_control->item[i].refcnt == 0)
> continue;
>
> /*
> * If the reference count is 1, the slot is still in use, but the
> * segment is in the process of going away. Treat that as if we
> * didn't find a match.
> */
> if (dsm_control->item[i].refcnt == 1)
> break;
>
> /* Otherwise, if the descriptor matches, we've found a match. */
> if (dsm_control->item[i].handle == seg->handle)
> {
> dsm_control->item[i].refcnt++;
> seg->control_slot = i;
> break;
> }
> }
>
> The break because of refcnt == 1 doesn't generally seem to be a good
> idea. Why are we bailing if there's *any* segment that's in the process
> of being removed? I think the check should be there *after* the
> dsm_control->item[i].handle == seg->handle check?

You are correct. Good catch.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company