postgres.git / summary / log / commit / refs

commit    fddf45b38097d14301d249fbeebca32e40233bd2
Author:   Robert Haas <rhaas@postgresql.org>
Date:     Wed Mar 29 13:44:29 2017 +0000

    Plug race in dsa_attach.
    
    With sufficiently bad luck, it was possible for a parallel worker to
    attempt attach to a DSA area after all other backends have detached
    from it, which is not legal.  If the worker had waited a little longer
    to get started, the DSM itself would have been destroyed, which is why
    this wasn't noticed before.
    
    Thomas Munro, per a report from Andreas Seltenreich
    
    Discussion: http://postgr.es/m/87h92g83t3.fsf@credativ.de


 src/backend/utils/mmgr/dsa.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/backend/utils/mmgr/dsa.c b/src/backend/utils/mmgr/dsa.c
index 6d5d12a6c9d..d08317249bb 100644
--- a/src/backend/utils/mmgr/dsa.c
+++ b/src/backend/utils/mmgr/dsa.c
@@ -1314,6 +1314,13 @@ attach_internal(void *place, dsm_segment *segment, dsa_handle handle)
 
 	/* Bump the reference count. */
 	LWLockAcquire(DSA_AREA_LOCK(area), LW_EXCLUSIVE);
+	if (control->refcnt == 0)
+	{
+		/* We can't attach to a DSA area that has already been destroyed. */
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("could not attach to dsa_area")));
+	}
 	++control->refcnt;
 	LWLockRelease(DSA_AREA_LOCK(area));
 


[parent: 3582b223d494]