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Commit82e861f

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committed
Fix LWLockAssign() so that it can safely be executed after postmaster
initialization. Add spinlocking, fix EXEC_BACKEND unsafeness.
1 parent77d1de3 commit82e861f

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2 files changed

+31
-15
lines changed

2 files changed

+31
-15
lines changed

‎src/backend/storage/ipc/shmem.c‎

Lines changed: 2 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/storage/ipc/shmem.c,v 1.85 2005/08/20 23:26:20 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/storage/ipc/shmem.c,v 1.86 2005/10/07 21:42:38 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -71,8 +71,7 @@ SHMEM_OFFSET ShmemBase;/* start address of shared memory */
7171

7272
staticSHMEM_OFFSETShmemEnd;/* end+1 address of shared memory */
7373

74-
NON_EXEC_STATICslock_t*ShmemLock;/* spinlock for shared memory
75-
* allocation */
74+
slock_t*ShmemLock;/* spinlock for shared memory and LWLock allocation */
7675

7776
NON_EXEC_STATICslock_t*ShmemIndexLock;/* spinlock for ShmemIndex */
7877

‎src/backend/storage/lmgr/lwlock.c‎

Lines changed: 29 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -15,7 +15,7 @@
1515
* Portions Copyright (c) 1994, Regents of the University of California
1616
*
1717
* IDENTIFICATION
18-
* $PostgreSQL: pgsql/src/backend/storage/lmgr/lwlock.c,v 1.31 2005/10/0720:11:03 tgl Exp $
18+
* $PostgreSQL: pgsql/src/backend/storage/lmgr/lwlock.c,v 1.32 2005/10/0721:42:38 tgl Exp $
1919
*
2020
*-------------------------------------------------------------------------
2121
*/
@@ -27,6 +27,10 @@
2727
#include"storage/spin.h"
2828

2929

30+
/* We use the ShmemLock spinlock to protect LWLockAssign */
31+
externslock_t*ShmemLock;
32+
33+
3034
typedefstructLWLock
3135
{
3236
slock_tmutex;/* Protects LWLock and queue of PGPROCs */
@@ -65,9 +69,6 @@ typedef union LWLockPadded
6569
*/
6670
NON_EXEC_STATICLWLockPadded*LWLockArray=NULL;
6771

68-
/* shared counter for dynamic allocation of LWLockIds */
69-
staticint*LWLockCounter;
70-
7172

7273
/*
7374
* We use this structure to keep track of locked LWLocks for release
@@ -159,7 +160,7 @@ LWLockShmemSize(void)
159160
/* Space for the LWLock array. */
160161
size=mul_size(numLocks,sizeof(LWLockPadded));
161162

162-
/* Space forshared allocation counter, plus room for alignment. */
163+
/* Space fordynamic allocation counter, plus room for alignment. */
163164
size=add_size(size,2*sizeof(int)+LWLOCK_PADDED_SIZE);
164165

165166
returnsize;
@@ -175,12 +176,16 @@ CreateLWLocks(void)
175176
intnumLocks=NumLWLocks();
176177
SizespaceLocks=LWLockShmemSize();
177178
LWLockPadded*lock;
179+
int*LWLockCounter;
178180
char*ptr;
179181
intid;
180182

181183
/* Allocate space */
182184
ptr= (char*)ShmemAlloc(spaceLocks);
183185

186+
/* Leave room for dynamic allocation counter */
187+
ptr+=2*sizeof(int);
188+
184189
/* Ensure desired alignment of LWLock array */
185190
ptr+=LWLOCK_PADDED_SIZE- ((unsigned long)ptr) %LWLOCK_PADDED_SIZE;
186191

@@ -200,9 +205,10 @@ CreateLWLocks(void)
200205
}
201206

202207
/*
203-
* Initialize the dynamic-allocation counter at the end of the array
208+
* Initialize the dynamic-allocation counter, which is stored just before
209+
* the first LWLock.
204210
*/
205-
LWLockCounter= (int*)lock;
211+
LWLockCounter= (int*)((char*)LWLockArray-2*sizeof(int));
206212
LWLockCounter[0]= (int)NumFixedLWLocks;
207213
LWLockCounter[1]=numLocks;
208214
}
@@ -211,16 +217,27 @@ CreateLWLocks(void)
211217
/*
212218
* LWLockAssign - assign a dynamically-allocated LWLock number
213219
*
214-
* NB: we do not currently try to interlock this. Could perhaps use
215-
* ShmemLock spinlock if there were any need to assign LWLockIds after
216-
* shmem setup.
220+
* We interlock this using the same spinlock that is used to protect
221+
* ShmemAlloc(). Interlocking is not really necessary during postmaster
222+
* startup, but it is needed if any user-defined code tries to allocate
223+
* LWLocks after startup.
217224
*/
218225
LWLockId
219226
LWLockAssign(void)
220227
{
228+
LWLockIdresult;
229+
int*LWLockCounter;
230+
231+
LWLockCounter= (int*) ((char*)LWLockArray-2*sizeof(int));
232+
SpinLockAcquire(ShmemLock);
221233
if (LWLockCounter[0] >=LWLockCounter[1])
222-
elog(FATAL,"no more LWLockIds available");
223-
return (LWLockId) (LWLockCounter[0]++);
234+
{
235+
SpinLockRelease(ShmemLock);
236+
elog(ERROR,"no more LWLockIds available");
237+
}
238+
result= (LWLockId) (LWLockCounter[0]++);
239+
SpinLockRelease(ShmemLock);
240+
returnresult;
224241
}
225242

226243

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