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Commita0d35eb

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Fix mislabeling of PROC_QUEUE->links as PGPROC, fixing UBSan on 32bit
ProcSleep() used a PGPROC* variable to point to PROC_QUEUE->links.next,because that does "the right thing" with SHMQueueInsertBefore(). While thatlargely works, it's certainly not correct and unnecessary - we can just useSHM_QUEUE* to point to the insertion point.Noticed when testing a 32bit of postgres with undefined behaviorsanitizer. UBSan noticed that sometimes the supposed PGPROC wasn'tsufficiently aligned (required since46d6e5f, ensured indirectly, viaShmemAllocRaw() guaranteeing cacheline alignment).For now fix this by using a SHM_QUEUE* for the insertion point. Subsequentlywe should replace all the use of PROC_QUEUE and SHM_QUEUE with ilist.h, butthat's a larger change that we don't want to backpatch.Backpatch to all supported versions - it's useful to be able to run postgresunder UBSan.Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>Discussion:https://postgr.es/m/20221117014230.op5kmgypdv2dtqsf@awork3.anarazel.deBackpatch: 11-
1 parentad08673 commita0d35eb

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  • src/backend/storage/lmgr

1 file changed

+14
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lines changed

‎src/backend/storage/lmgr/proc.c‎

Lines changed: 14 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -1050,13 +1050,13 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
10501050
uint32hashcode=locallock->hashcode;
10511051
LWLock*partitionLock=LockHashPartitionLock(hashcode);
10521052
PROC_QUEUE*waitQueue=&(lock->waitProcs);
1053+
SHM_QUEUE*waitQueuePos;
10531054
LOCKMASKmyHeldLocks=MyProc->heldLocks;
10541055
TimestampTzstandbyWaitStart=0;
10551056
boolearly_deadlock= false;
10561057
boolallow_autovacuum_cancel= true;
10571058
boollogged_recovery_conflict= false;
10581059
ProcWaitStatusmyWaitStatus;
1059-
PGPROC*proc;
10601060
PGPROC*leader=MyProc->lockGroupLeader;
10611061
inti;
10621062

@@ -1104,21 +1104,24 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
11041104
* we are only considering the part of the wait queue before my insertion
11051105
* point.
11061106
*/
1107-
if (myHeldLocks!=0)
1107+
if (myHeldLocks!=0&&waitQueue->size>0)
11081108
{
11091109
LOCKMASKaheadRequests=0;
1110+
SHM_QUEUE*proc_node;
11101111

1111-
proc= (PGPROC*)waitQueue->links.next;
1112+
proc_node=waitQueue->links.next;
11121113
for (i=0;i<waitQueue->size;i++)
11131114
{
1115+
PGPROC*proc= (PGPROC*)proc_node;
1116+
11141117
/*
11151118
* If we're part of the same locking group as this waiter, its
11161119
* locks neither conflict with ours nor contribute to
11171120
* aheadRequests.
11181121
*/
11191122
if (leader!=NULL&&leader==proc->lockGroupLeader)
11201123
{
1121-
proc= (PGPROC*)proc->links.next;
1124+
proc_node=proc->links.next;
11221125
continue;
11231126
}
11241127
/* Must he wait for me? */
@@ -1153,24 +1156,25 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
11531156
}
11541157
/* Nope, so advance to next waiter */
11551158
aheadRequests |=LOCKBIT_ON(proc->waitLockMode);
1156-
proc= (PGPROC*)proc->links.next;
1159+
proc_node=proc->links.next;
11571160
}
11581161

11591162
/*
1160-
* If wefall out of loop normally, proc points towaitQueue head, so
1161-
* we will insert at tail of queue as desired.
1163+
* If weiterated through the whole queue, cur points tothe waitQueue
1164+
*head, sowe will insert at tail of queue as desired.
11621165
*/
1166+
waitQueuePos=proc_node;
11631167
}
11641168
else
11651169
{
11661170
/* I hold no locks, so I can't push in front of anyone. */
1167-
proc=(PGPROC*)&(waitQueue->links);
1171+
waitQueuePos=&waitQueue->links;
11681172
}
11691173

11701174
/*
1171-
* Insert self into queue,ahead ofthegiven proc (or at tail of queue).
1175+
* Insert self into queue,attheposition determined above.
11721176
*/
1173-
SHMQueueInsertBefore(&(proc->links),&(MyProc->links));
1177+
SHMQueueInsertBefore(waitQueuePos,&MyProc->links);
11741178
waitQueue->size++;
11751179

11761180
lock->waitMask |=LOCKBIT_ON(lockmode);

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