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Commitfc41542

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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 parentbb3f42a commitfc41542

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1 file changed

+14
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lines changed
  • src/backend/storage/lmgr

1 file changed

+14
-10
lines changed

‎src/backend/storage/lmgr/proc.c

Lines changed: 14 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -1074,13 +1074,13 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
10741074
uint32hashcode=locallock->hashcode;
10751075
LWLock*partitionLock=LockHashPartitionLock(hashcode);
10761076
PROC_QUEUE*waitQueue=&(lock->waitProcs);
1077+
SHM_QUEUE*waitQueuePos;
10771078
LOCKMASKmyHeldLocks=MyProc->heldLocks;
10781079
TimestampTzstandbyWaitStart=0;
10791080
boolearly_deadlock= false;
10801081
boolallow_autovacuum_cancel= true;
10811082
boollogged_recovery_conflict= false;
10821083
ProcWaitStatusmyWaitStatus;
1083-
PGPROC*proc;
10841084
PGPROC*leader=MyProc->lockGroupLeader;
10851085
inti;
10861086

@@ -1128,21 +1128,24 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
11281128
* we are only considering the part of the wait queue before my insertion
11291129
* point.
11301130
*/
1131-
if (myHeldLocks!=0)
1131+
if (myHeldLocks!=0&&waitQueue->size>0)
11321132
{
11331133
LOCKMASKaheadRequests=0;
1134+
SHM_QUEUE*proc_node;
11341135

1135-
proc= (PGPROC*)waitQueue->links.next;
1136+
proc_node=waitQueue->links.next;
11361137
for (i=0;i<waitQueue->size;i++)
11371138
{
1139+
PGPROC*proc= (PGPROC*)proc_node;
1140+
11381141
/*
11391142
* If we're part of the same locking group as this waiter, its
11401143
* locks neither conflict with ours nor contribute to
11411144
* aheadRequests.
11421145
*/
11431146
if (leader!=NULL&&leader==proc->lockGroupLeader)
11441147
{
1145-
proc= (PGPROC*)proc->links.next;
1148+
proc_node=proc->links.next;
11461149
continue;
11471150
}
11481151
/* Must he wait for me? */
@@ -1177,24 +1180,25 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
11771180
}
11781181
/* Nope, so advance to next waiter */
11791182
aheadRequests |=LOCKBIT_ON(proc->waitLockMode);
1180-
proc= (PGPROC*)proc->links.next;
1183+
proc_node=proc->links.next;
11811184
}
11821185

11831186
/*
1184-
* If wefall out of loop normally, proc points towaitQueue head, so
1185-
* we will insert at tail of queue as desired.
1187+
* If weiterated through the whole queue, cur points tothe waitQueue
1188+
*head, sowe will insert at tail of queue as desired.
11861189
*/
1190+
waitQueuePos=proc_node;
11871191
}
11881192
else
11891193
{
11901194
/* I hold no locks, so I can't push in front of anyone. */
1191-
proc=(PGPROC*)&(waitQueue->links);
1195+
waitQueuePos=&waitQueue->links;
11921196
}
11931197

11941198
/*
1195-
* Insert self into queue,ahead ofthegiven proc (or at tail of queue).
1199+
* Insert self into queue,attheposition determined above.
11961200
*/
1197-
SHMQueueInsertBefore(&(proc->links),&(MyProc->links));
1201+
SHMQueueInsertBefore(waitQueuePos,&MyProc->links);
11981202
waitQueue->size++;
11991203

12001204
lock->waitMask |=LOCKBIT_ON(lockmode);

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