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Commit4cbcb7e

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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 parent80cd1a6 commit4cbcb7e

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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
@@ -1068,11 +1068,11 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
10681068
uint32hashcode=locallock->hashcode;
10691069
LWLock*partitionLock=LockHashPartitionLock(hashcode);
10701070
PROC_QUEUE*waitQueue=&(lock->waitProcs);
1071+
SHM_QUEUE*waitQueuePos;
10711072
LOCKMASKmyHeldLocks=MyProc->heldLocks;
10721073
boolearly_deadlock= false;
10731074
boolallow_autovacuum_cancel= true;
10741075
intmyWaitStatus;
1075-
PGPROC*proc;
10761076
PGPROC*leader=MyProc->lockGroupLeader;
10771077
inti;
10781078

@@ -1114,21 +1114,24 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
11141114
* we are only considering the part of the wait queue before my insertion
11151115
* point.
11161116
*/
1117-
if (myHeldLocks!=0)
1117+
if (myHeldLocks!=0&&waitQueue->size>0)
11181118
{
11191119
LOCKMASKaheadRequests=0;
1120+
SHM_QUEUE*proc_node;
11201121

1121-
proc= (PGPROC*)waitQueue->links.next;
1122+
proc_node=waitQueue->links.next;
11221123
for (i=0;i<waitQueue->size;i++)
11231124
{
1125+
PGPROC*proc= (PGPROC*)proc_node;
1126+
11241127
/*
11251128
* If we're part of the same locking group as this waiter, its
11261129
* locks neither conflict with ours nor contribute to
11271130
* aheadRequests.
11281131
*/
11291132
if (leader!=NULL&&leader==proc->lockGroupLeader)
11301133
{
1131-
proc= (PGPROC*)proc->links.next;
1134+
proc_node=proc->links.next;
11321135
continue;
11331136
}
11341137
/* Must he wait for me? */
@@ -1165,24 +1168,25 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
11651168
}
11661169
/* Nope, so advance to next waiter */
11671170
aheadRequests |=LOCKBIT_ON(proc->waitLockMode);
1168-
proc= (PGPROC*)proc->links.next;
1171+
proc_node=proc->links.next;
11691172
}
11701173

11711174
/*
1172-
* If wefall out of loop normally, proc points towaitQueue head, so
1173-
* we will insert at tail of queue as desired.
1175+
* If weiterated through the whole queue, cur points tothe waitQueue
1176+
*head, sowe will insert at tail of queue as desired.
11741177
*/
1178+
waitQueuePos=proc_node;
11751179
}
11761180
else
11771181
{
11781182
/* I hold no locks, so I can't push in front of anyone. */
1179-
proc=(PGPROC*)&(waitQueue->links);
1183+
waitQueuePos=&waitQueue->links;
11801184
}
11811185

11821186
/*
1183-
* Insert self into queue,ahead ofthegiven proc (or at tail of queue).
1187+
* Insert self into queue,attheposition determined above.
11841188
*/
1185-
SHMQueueInsertBefore(&(proc->links),&(MyProc->links));
1189+
SHMQueueInsertBefore(waitQueuePos,&MyProc->links);
11861190
waitQueue->size++;
11871191

11881192
lock->waitMask |=LOCKBIT_ON(lockmode);

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