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Fix logic bug in dsm_attach().

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The previous coding would potentially cause attaching to segment A to
fail if segment B was at the same time in the process of going away.

Andres Freund, with a comment tweak by me
This commit is contained in:
Robert Haas 2014-05-06 13:37:46 -04:00
parent 4335c95815
commit e0124230ba
1 changed files with 8 additions and 7 deletions
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15
src/backend/storage/ipc/dsm.c
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@ -566,6 +566,10 @@ dsm_attach(dsm_handle h)
if (dsm_control->item[i].refcnt == 0)
continue;
/* If the handle doesn't match, it's not the slot we want. */
if (dsm_control->item[i].handle != seg->handle)
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
@ -574,13 +578,10 @@ dsm_attach(dsm_handle h)
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;
}
/* Otherwise we've found a match. */
dsm_control->item[i].refcnt++;
seg->control_slot = i;
break;
}
LWLockRelease(DynamicSharedMemoryControlLock);