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Tighten up error recovery for fast-path locking. 

The previous code could cause a backend crash after BEGIN; SAVEPOINT a;
LOCK TABLE foo (interrupted by ^C or statement timeout); ROLLBACK TO
SAVEPOINT a; LOCK TABLE foo, and might have leaked strong-lock counts
in other situations.

Report by Zoltán Böszörményi; patch review by Jeff Davis.
This commit is contained in:
Robert Haas 2012-04-18 11:17:30 -04:00
parent ab77b2da8b
commit 53c5b869b4
7 changed files with 94 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/backend/access/transam/xact.c
View File

@ -2259,7 +2259,7 @@ AbortTransaction(void)
* Also clean up any open wait for lock, since the lock manager will choke
* if we try to wait for another lock before doing this.
*/
LockWaitCancel();
LockErrorCleanup();
/*
* check the current transaction state
@ -4144,7 +4144,7 @@ AbortSubTransaction(void)
AbortBufferIO();
UnlockBuffers();
LockWaitCancel();
LockErrorCleanup();
/*
* check the current transaction state

2
src/backend/storage/lmgr/README
View File

@ -560,7 +560,7 @@ examines every member of the wait queue (this was not true in the 7.0
implementation, BTW). Therefore, if ProcLockWakeup is always invoked
after a lock is released or a wait queue is rearranged, there can be no
failure to wake a wakable process. One should also note that
LockWaitCancel (abort a waiter due to outside factors) must run
LockErrorCleanup (abort a waiter due to outside factors) must run
ProcLockWakeup, in case the canceled waiter was soft-blocking other
waiters.

91
src/backend/storage/lmgr/lock.c
View File

@ -250,7 +250,8 @@ static HTAB *LockMethodProcLockHash;
static HTAB *LockMethodLocalHash;
/* private state for GrantAwaitedLock */
/* private state for error cleanup */
static LOCALLOCK *StrongLockInProgress;
static LOCALLOCK *awaitedLock;
static ResourceOwner awaitedOwner;
@ -338,6 +339,8 @@ static void RemoveLocalLock(LOCALLOCK *locallock);
static PROCLOCK *SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc,
const LOCKTAG *locktag, uint32 hashcode, LOCKMODE lockmode);
static void GrantLockLocal(LOCALLOCK *locallock, ResourceOwner owner);
static void BeginStrongLockAcquire(LOCALLOCK *locallock, uint32 fasthashcode);
static void FinishStrongLockAcquire(void);
static void WaitOnLock(LOCALLOCK *locallock, ResourceOwner owner);
static void ReleaseLockForOwner(LOCALLOCK *locallock, ResourceOwner owner);
static bool UnGrantLock(LOCK *lock, LOCKMODE lockmode,
@ -738,22 +741,11 @@ LockAcquireExtended(const LOCKTAG *locktag,
}
else if (FastPathStrongMode(lockmode))
{
/*
* Adding to a memory location is not atomic, so we take a
* spinlock to ensure we don't collide with someone else trying
* to bump the count at the same time.
*
* XXX: It might be worth considering using an atomic fetch-and-add
* instruction here, on architectures where that is supported.
*/
Assert(locallock->holdsStrongLockCount == FALSE);
SpinLockAcquire(&FastPathStrongRelationLocks->mutex);
FastPathStrongRelationLocks->count[fasthashcode]++;
locallock->holdsStrongLockCount = TRUE;
SpinLockRelease(&FastPathStrongRelationLocks->mutex);
BeginStrongLockAcquire(locallock, fasthashcode);
if (!FastPathTransferRelationLocks(lockMethodTable, locktag,
hashcode))
{
AbortStrongLockAcquire();
if (reportMemoryError)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
@ -779,6 +771,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
hashcode, lockmode);
if (!proclock)
{
AbortStrongLockAcquire();
LWLockRelease(partitionLock);
if (reportMemoryError)
ereport(ERROR,
@ -820,6 +813,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
*/
if (dontWait)
{
AbortStrongLockAcquire();
if (proclock->holdMask == 0)
{
uint32 proclock_hashcode;
@ -884,6 +878,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
*/
if (!(proclock->holdMask & LOCKBIT_ON(lockmode)))
{
AbortStrongLockAcquire();
PROCLOCK_PRINT("LockAcquire: INCONSISTENT", proclock);
LOCK_PRINT("LockAcquire: INCONSISTENT", lock, lockmode);
/* Should we retry ? */
@ -894,6 +889,12 @@ LockAcquireExtended(const LOCKTAG *locktag,
LOCK_PRINT("LockAcquire: granted", lock, lockmode);
}
/*
* Lock state is fully up-to-date now; if we error out after this, no
* special error cleanup is required.
*/
FinishStrongLockAcquire();
LWLockRelease(partitionLock);
/*
@ -1349,6 +1350,64 @@ GrantLockLocal(LOCALLOCK *locallock, ResourceOwner owner)
locallock->numLockOwners++;
}
/*
* BeginStrongLockAcquire - inhibit use of fastpath for a given LOCALLOCK,
* and arrange for error cleanup if it fails
*/
static void
BeginStrongLockAcquire(LOCALLOCK *locallock, uint32 fasthashcode)
{
Assert(StrongLockInProgress == NULL);
Assert(locallock->holdsStrongLockCount == FALSE);
/*
* Adding to a memory location is not atomic, so we take a
* spinlock to ensure we don't collide with someone else trying
* to bump the count at the same time.
*
* XXX: It might be worth considering using an atomic fetch-and-add
* instruction here, on architectures where that is supported.
*/
SpinLockAcquire(&FastPathStrongRelationLocks->mutex);
FastPathStrongRelationLocks->count[fasthashcode]++;
locallock->holdsStrongLockCount = TRUE;
StrongLockInProgress = locallock;
SpinLockRelease(&FastPathStrongRelationLocks->mutex);
}
/*
* FinishStrongLockAcquire - cancel pending cleanup for a strong lock
* acquisition once it's no longer needed
*/
static void
FinishStrongLockAcquire(void)
{
StrongLockInProgress = NULL;
}
/*
* AbortStrongLockAcquire - undo strong lock state changes performed by
* BeginStrongLockAcquire.
*/
void
AbortStrongLockAcquire(void)
{
uint32 fasthashcode;
LOCALLOCK *locallock = StrongLockInProgress;
if (locallock == NULL)
return;
fasthashcode = FastPathStrongLockHashPartition(locallock->hashcode);
Assert(locallock->holdsStrongLockCount == TRUE);
SpinLockAcquire(&FastPathStrongRelationLocks->mutex);
FastPathStrongRelationLocks->count[fasthashcode]--;
locallock->holdsStrongLockCount = FALSE;
StrongLockInProgress = NULL;
SpinLockRelease(&FastPathStrongRelationLocks->mutex);
}
/*
* GrantAwaitedLock -- call GrantLockLocal for the lock we are doing
* WaitOnLock on.
@ -1414,7 +1473,7 @@ WaitOnLock(LOCALLOCK *locallock, ResourceOwner owner)
* We can and do use a PG_TRY block to try to clean up after failure, but
* this still has a major limitation: elog(FATAL) can occur while waiting
* (eg, a "die" interrupt), and then control won't come back here. So all
* cleanup of essential state should happen in LockWaitCancel, not here.
* cleanup of essential state should happen in LockErrorCleanup, not here.
* We can use PG_TRY to clear the "waiting" status flags, since doing that
* is unimportant if the process exits.
*/
@ -1441,7 +1500,7 @@ WaitOnLock(LOCALLOCK *locallock, ResourceOwner owner)
}
PG_CATCH();
{
/* In this path, awaitedLock remains set until LockWaitCancel */
/* In this path, awaitedLock remains set until LockErrorCleanup */
/* Report change to non-waiting status */
pgstat_report_waiting(false);

19
src/backend/storage/lmgr/proc.c
View File

@ -635,17 +635,20 @@ IsWaitingForLock(void)
}
/*
* Cancel any pending wait for lock, when aborting a transaction.
* Cancel any pending wait for lock, when aborting a transaction, and revert
* any strong lock count acquisition for a lock being acquired.
*
* (Normally, this would only happen if we accept a cancel/die
* interrupt while waiting; but an ereport(ERROR) while waiting is
* within the realm of possibility, too.)
* interrupt while waiting; but an ereport(ERROR) before or during the lock
* wait is within the realm of possibility, too.)
*/
void
LockWaitCancel(void)
LockErrorCleanup(void)
{
LWLockId partitionLock;
AbortStrongLockAcquire();
/* Nothing to do if we weren't waiting for a lock */
if (lockAwaited == NULL)
return;
@ -709,7 +712,7 @@ ProcReleaseLocks(bool isCommit)
if (!MyProc)
return;
/* If waiting, get off wait queue (should only be needed after error) */
LockWaitCancel();
LockErrorCleanup();
/* Release locks */
LockReleaseAll(DEFAULT_LOCKMETHOD, !isCommit);
@ -1019,7 +1022,7 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
* NOTE: this may also cause us to exit critical-section state, possibly
* allowing a cancel/die interrupt to be accepted. This is OK because we
* have recorded the fact that we are waiting for a lock, and so
* LockWaitCancel will clean up if cancel/die happens.
* LockErrorCleanup will clean up if cancel/die happens.
*/
LWLockRelease(partitionLock);
@ -1062,7 +1065,7 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
* don't, because we have no shared-state-change work to do after being
* granted the lock (the grantor did it all). We do have to worry about
* updating the locallock table, but if we lose control to an error,
* LockWaitCancel will fix that up.
* LockErrorCleanup will fix that up.
*/
do
{
@ -1207,7 +1210,7 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
LWLockAcquire(partitionLock, LW_EXCLUSIVE);
/*
* We no longer want LockWaitCancel to do anything.
* We no longer want LockErrorCleanup to do anything.
*/
lockAwaited = NULL;

6
src/backend/tcop/postgres.c
View File

@ -2575,7 +2575,7 @@ die(SIGNAL_ARGS)
/* bump holdoff count to make ProcessInterrupts() a no-op */
/* until we are done getting ready for it */
InterruptHoldoffCount++;
LockWaitCancel(); /* prevent CheckDeadLock from running */
LockErrorCleanup(); /* prevent CheckDeadLock from running */
DisableNotifyInterrupt();
DisableCatchupInterrupt();
InterruptHoldoffCount--;
@ -2617,7 +2617,7 @@ StatementCancelHandler(SIGNAL_ARGS)
/* bump holdoff count to make ProcessInterrupts() a no-op */
/* until we are done getting ready for it */
InterruptHoldoffCount++;
LockWaitCancel(); /* prevent CheckDeadLock from running */
LockErrorCleanup(); /* prevent CheckDeadLock from running */
DisableNotifyInterrupt();
DisableCatchupInterrupt();
InterruptHoldoffCount--;
@ -2776,7 +2776,7 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
/* bump holdoff count to make ProcessInterrupts() a no-op */
/* until we are done getting ready for it */
InterruptHoldoffCount++;
LockWaitCancel(); /* prevent CheckDeadLock from running */
LockErrorCleanup(); /* prevent CheckDeadLock from running */
DisableNotifyInterrupt();
DisableCatchupInterrupt();
InterruptHoldoffCount--;

1
src/include/storage/lock.h
View File

@ -489,6 +489,7 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag,
bool sessionLock,
bool dontWait,
bool report_memory_error);
extern void AbortStrongLockAcquire(void);
extern bool LockRelease(const LOCKTAG *locktag,
LOCKMODE lockmode, bool sessionLock);
extern void LockReleaseSession(LOCKMETHODID lockmethodid);

2
src/include/storage/proc.h
View File

@ -244,7 +244,7 @@ extern int ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable);
extern PGPROC *ProcWakeup(PGPROC *proc, int waitStatus);
extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock);
extern bool IsWaitingForLock(void);
extern void LockWaitCancel(void);
extern void LockErrorCleanup(void);
extern void ProcWaitForSignal(void);
extern void ProcSendSignal(int pid);