possible dsm bug in dsm_attach()

Hi,

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?

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services