database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-11-09 06:21:09 +03:00
Code Activity

Avoid bogus TwoPhaseState locking sequences

Browse Source 
The optimized code in 728bd991c3 contains a few invalid locking
sequences.  To wit, the original code would try to acquire an lwlock
that it already holds.  Avoid this by moving lock acquisitions to
higher-level code, and install appropriate assertions in low-level that
the correct mode is held.

Authors: Michael Paquier, Álvaro Herrera
Reported-By: chuanting wang
Bug: #14680
Discussion: https://postgr.es/m/20170531033228.1487.10124@wrigleys.postgresql.org
This commit is contained in:
Alvaro Herrera
2017-06-14 11:29:05 -04:00
parent 0d9bdbcaae
commit e90ceeaa49
2 changed files with 85 additions and 74 deletions
Download Patch File Download Diff File Expand all files Collapse all files

87
src/backend/access/transam/twophase.c
View File

@@ -195,7 +195,10 @@ typedef struct TwoPhaseStateData
static TwoPhaseStateData *TwoPhaseState;
/*
* Global transaction entry currently locked by us, if any.
* Global transaction entry currently locked by us, if any. Note that any
* access to the entry pointed to by this variable must be protected by
* TwoPhaseStateLock, though obviously the pointer itself doesn't need to be
* (since it's just local memory).
*/
static GlobalTransaction MyLockedGxact = NULL;
@@ -338,18 +341,13 @@ AtAbort_Twophase(void)
* resources held by the transaction yet. In those cases, the in-memory
* state can be wrong, but it's too late to back out.
*/
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
if (!MyLockedGxact->valid)
{
RemoveGXact(MyLockedGxact);
}
else
{
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
MyLockedGxact->locking_backend = InvalidBackendId;
LWLockRelease(TwoPhaseStateLock);
LWLockRelease(TwoPhaseStateLock);
}
MyLockedGxact = NULL;
}
@@ -454,6 +452,8 @@ MarkAsPreparingGuts(GlobalTransaction gxact, TransactionId xid, const char *gid,
PGXACT *pgxact;
int i;
Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
Assert(gxact != NULL);
proc = &ProcGlobal->allProcs[gxact->pgprocno];
pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
@@ -530,15 +530,19 @@ GXactLoadSubxactData(GlobalTransaction gxact, int nsubxacts,
/*
* MarkAsPrepared
* Mark the GXACT as fully valid, and enter it into the global ProcArray.
*
* lock_held indicates whether caller already holds TwoPhaseStateLock.
*/
static void
MarkAsPrepared(GlobalTransaction gxact)
MarkAsPrepared(GlobalTransaction gxact, bool lock_held)
{
/* Lock here may be overkill, but I'm not convinced of that ... */
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
if (!lock_held)
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
Assert(!gxact->valid);
gxact->valid = true;
LWLockRelease(TwoPhaseStateLock);
if (!lock_held)
LWLockRelease(TwoPhaseStateLock);
/*
* Put it into the global ProcArray so TransactionIdIsInProgress considers
@@ -632,7 +636,7 @@ RemoveGXact(GlobalTransaction gxact)
{
int i;
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
{
@@ -646,14 +650,10 @@ RemoveGXact(GlobalTransaction gxact)
gxact->next = TwoPhaseState->freeGXacts;
TwoPhaseState->freeGXacts = gxact;
LWLockRelease(TwoPhaseStateLock);
return;
}
}
LWLockRelease(TwoPhaseStateLock);
elog(ERROR, "failed to find %p in GlobalTransaction array", gxact);
}
@@ -1127,7 +1127,7 @@ EndPrepare(GlobalTransaction gxact)
* the xact crashed. Instead we have a window where the same XID appears
* twice in ProcArray, which is OK.
*/
MarkAsPrepared(gxact);
MarkAsPrepared(gxact, false);
/*
* Now we can mark ourselves as out of the commit critical section: a
@@ -1506,7 +1506,9 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
if (gxact->ondisk)
RemoveTwoPhaseFile(xid, true);
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
RemoveGXact(gxact);
LWLockRelease(TwoPhaseStateLock);
MyLockedGxact = NULL;
pfree(buf);
@@ -1734,6 +1736,7 @@ restoreTwoPhaseData(void)
struct dirent *clde;
cldir = AllocateDir(TWOPHASE_DIR);
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
while ((clde = ReadDir(cldir, TWOPHASE_DIR)) != NULL)
{
if (strlen(clde->d_name) == 8 &&
@@ -1752,6 +1755,7 @@ restoreTwoPhaseData(void)
PrepareRedoAdd(buf, InvalidXLogRecPtr, InvalidXLogRecPtr);
}
}
LWLockRelease(TwoPhaseStateLock);
FreeDir(cldir);
}
@@ -1792,7 +1796,7 @@ PrescanPreparedTransactions(TransactionId **xids_p, int *nxids_p)
int allocsize = 0;
int i;
LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
{
TransactionId xid;
@@ -1867,7 +1871,7 @@ StandbyRecoverPreparedTransactions(void)
{
int i;
LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
{
TransactionId xid;
@@ -1893,7 +1897,8 @@ StandbyRecoverPreparedTransactions(void)
* Scan the shared memory entries of TwoPhaseState and reload the state for
* each prepared transaction (reacquire locks, etc).
*
* This is run during database startup.
* This is run at the end of recovery, but before we allow backends to write
* WAL.
*
* At the end of recovery the way we take snapshots will change. We now need
* to mark all running transactions with their full SubTransSetParent() info
@@ -1907,9 +1912,7 @@ RecoverPreparedTransactions(void)
{
int i;
/*
* Don't need a lock in the recovery phase.
*/
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
{
TransactionId xid;
@@ -1955,7 +1958,6 @@ RecoverPreparedTransactions(void)
* Recreate its GXACT and dummy PGPROC. But, check whether it was
* added in redo and already has a shmem entry for it.
*/
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
MarkAsPreparingGuts(gxact, xid, gid,
hdr->prepared_at,
hdr->owner, hdr->database);
@@ -1963,13 +1965,13 @@ RecoverPreparedTransactions(void)
/* recovered, so reset the flag for entries generated by redo */
gxact->inredo = false;
GXactLoadSubxactData(gxact, hdr->nsubxacts, subxids);
MarkAsPrepared(gxact, true);
LWLockRelease(TwoPhaseStateLock);
GXactLoadSubxactData(gxact, hdr->nsubxacts, subxids);
MarkAsPrepared(gxact);
/*
* Recover other state (notably locks) using resource managers
* Recover other state (notably locks) using resource managers.
*/
ProcessRecords(bufptr, xid, twophase_recover_callbacks);
@@ -1988,7 +1990,11 @@ RecoverPreparedTransactions(void)
PostPrepare_Twophase();
pfree(buf);
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
}
LWLockRelease(TwoPhaseStateLock);
}
/*
@@ -2014,6 +2020,8 @@ ProcessTwoPhaseBuffer(TransactionId xid,
TwoPhaseFileHeader *hdr;
int i;
Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
if (!fromdisk)
Assert(prepare_start_lsn != InvalidXLogRecPtr);
@@ -2030,8 +2038,8 @@ ProcessTwoPhaseBuffer(TransactionId xid,
else
{
ereport(WARNING,
(errmsg("removing stale two-phase state from"
" shared memory for \"%u\"", xid)));
(errmsg("removing stale two-phase state from shared memory for \"%u\"",
xid)));
PrepareRedoRemove(xid, true);
}
return NULL;
@@ -2308,6 +2316,7 @@ PrepareRedoAdd(char *buf, XLogRecPtr start_lsn, XLogRecPtr end_lsn)
const char *gid;
GlobalTransaction gxact;
Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
Assert(RecoveryInProgress());
bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader));
@@ -2324,7 +2333,6 @@ PrepareRedoAdd(char *buf, XLogRecPtr start_lsn, XLogRecPtr end_lsn)
* that it got added in the redo phase
*/
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
/* Get a free gxact from the freelist */
if (TwoPhaseState->freeGXacts == NULL)
ereport(ERROR,
@@ -2350,17 +2358,17 @@ PrepareRedoAdd(char *buf, XLogRecPtr start_lsn, XLogRecPtr end_lsn)
Assert(TwoPhaseState->numPrepXacts < max_prepared_xacts);
TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts++] = gxact;
LWLockRelease(TwoPhaseStateLock);
elog(DEBUG2, "Adding 2PC data to shared memory %u", gxact->xid);
elog(DEBUG2, "added 2PC data in shared memory for transaction %u", gxact->xid);
}
/*
* PrepareRedoRemove
*
* Remove the corresponding gxact entry from TwoPhaseState. Also
* remove the 2PC file if a prepared transaction was saved via
* an earlier checkpoint.
* Remove the corresponding gxact entry from TwoPhaseState. Also remove
* the 2PC file if a prepared transaction was saved via an earlier checkpoint.
*
* Caller must hold TwoPhaseStateLock in exclusive mode, because TwoPhaseState
* is updated.
*/
void
PrepareRedoRemove(TransactionId xid, bool giveWarning)
@@ -2369,9 +2377,9 @@ PrepareRedoRemove(TransactionId xid, bool giveWarning)
int i;
bool found = false;
Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
Assert(RecoveryInProgress());
LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
{
gxact = TwoPhaseState->prepXacts[i];
@@ -2383,7 +2391,6 @@ PrepareRedoRemove(TransactionId xid, bool giveWarning)
break;
}
}
LWLockRelease(TwoPhaseStateLock);
/*
* Just leave if there is nothing, this is expected during WAL replay.
@@ -2394,7 +2401,7 @@ PrepareRedoRemove(TransactionId xid, bool giveWarning)
/*
* And now we can clean up any files we may have left.
*/
elog(DEBUG2, "Removing 2PC data from shared memory %u", xid);
elog(DEBUG2, "removing 2PC data for transaction %u", xid);
if (gxact->ondisk)
RemoveTwoPhaseFile(xid, giveWarning);
RemoveGXact(gxact);