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Commitc13667b

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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 parentd3d3888 commitc13667b

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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
@@ -1067,11 +1067,11 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
10671067
uint32hashcode=locallock->hashcode;
10681068
LWLock*partitionLock=LockHashPartitionLock(hashcode);
10691069
PROC_QUEUE*waitQueue=&(lock->waitProcs);
1070+
SHM_QUEUE*waitQueuePos;
10701071
LOCKMASKmyHeldLocks=MyProc->heldLocks;
10711072
boolearly_deadlock= false;
10721073
boolallow_autovacuum_cancel= true;
10731074
intmyWaitStatus;
1074-
PGPROC*proc;
10751075
PGPROC*leader=MyProc->lockGroupLeader;
10761076
inti;
10771077

@@ -1119,21 +1119,24 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
11191119
* we are only considering the part of the wait queue before my insertion
11201120
* point.
11211121
*/
1122-
if (myHeldLocks!=0)
1122+
if (myHeldLocks!=0&&waitQueue->size>0)
11231123
{
11241124
LOCKMASKaheadRequests=0;
1125+
SHM_QUEUE*proc_node;
11251126

1126-
proc= (PGPROC*)waitQueue->links.next;
1127+
proc_node=waitQueue->links.next;
11271128
for (i=0;i<waitQueue->size;i++)
11281129
{
1130+
PGPROC*proc= (PGPROC*)proc_node;
1131+
11291132
/*
11301133
* If we're part of the same locking group as this waiter, its
11311134
* locks neither conflict with ours nor contribute to
11321135
* aheadRequests.
11331136
*/
11341137
if (leader!=NULL&&leader==proc->lockGroupLeader)
11351138
{
1136-
proc= (PGPROC*)proc->links.next;
1139+
proc_node=proc->links.next;
11371140
continue;
11381141
}
11391142
/* Must he wait for me? */
@@ -1168,24 +1171,25 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
11681171
}
11691172
/* Nope, so advance to next waiter */
11701173
aheadRequests |=LOCKBIT_ON(proc->waitLockMode);
1171-
proc= (PGPROC*)proc->links.next;
1174+
proc_node=proc->links.next;
11721175
}
11731176

11741177
/*
1175-
* If wefall out of loop normally, proc points towaitQueue head, so
1176-
* we will insert at tail of queue as desired.
1178+
* If weiterated through the whole queue, cur points tothe waitQueue
1179+
*head, sowe will insert at tail of queue as desired.
11771180
*/
1181+
waitQueuePos=proc_node;
11781182
}
11791183
else
11801184
{
11811185
/* I hold no locks, so I can't push in front of anyone. */
1182-
proc=(PGPROC*)&(waitQueue->links);
1186+
waitQueuePos=&waitQueue->links;
11831187
}
11841188

11851189
/*
1186-
* Insert self into queue,ahead ofthegiven proc (or at tail of queue).
1190+
* Insert self into queue,attheposition determined above.
11871191
*/
1188-
SHMQueueInsertBefore(&(proc->links),&(MyProc->links));
1192+
SHMQueueInsertBefore(waitQueuePos,&MyProc->links);
11891193
waitQueue->size++;
11901194

11911195
lock->waitMask |=LOCKBIT_ON(lockmode);

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