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Postgres FD Implementation
Commit e90ceeaa authored by Alvaro Herrera's avatar Alvaro Herrera
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Avoid bogus TwoPhaseState locking sequences 

The optimized code in 728bd991 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
parent 0d9bdbca
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Showing with 83 additions and 72 deletions
src/backend/access/transam/twophase.c
View file @ e90ceeaa
......@@ -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);
}
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];
......@@ -530,14 +530,18 @@ 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 ... */
if (!lock_held)
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
Assert(!gxact->valid);
gxact->valid = true;
if (!lock_held)
LWLockRelease(TwoPhaseStateLock);
/*
......@@ -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;
LWLockRelease(TwoPhaseStateLock);
GXactLoadSubxactData(gxact, hdr->nsubxacts, subxids);
MarkAsPrepared(gxact);
MarkAsPrepared(gxact, true);
LWLockRelease(TwoPhaseStateLock);
/*
* 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);
......
src/backend/access/transam/xact.c
View file @ e90ceeaa
......@@ -5351,6 +5351,8 @@ xact_redo_commit(xl_xact_parsed_commit *parsed,
int i;
TimestampTz commit_time;
Assert(TransactionIdIsValid(xid));
max_xid = TransactionIdLatest(xid, parsed->nsubxacts, parsed->subxacts);
/*
......@@ -5518,6 +5520,8 @@ xact_redo_abort(xl_xact_parsed_abort *parsed, TransactionId xid)
int i;
TransactionId max_xid;
Assert(TransactionIdIsValid(xid));
/*
* Make sure nextXid is beyond any XID mentioned in the record.
*
......@@ -5598,51 +5602,49 @@ xact_redo(XLogReaderState *record)
/* Backup blocks are not used in xact records */
Assert(!XLogRecHasAnyBlockRefs(record));
if (info == XLOG_XACT_COMMIT || info == XLOG_XACT_COMMIT_PREPARED)
if (info == XLOG_XACT_COMMIT)
{
xl_xact_commit *xlrec = (xl_xact_commit *) XLogRecGetData(record);
xl_xact_parsed_commit parsed;
ParseCommitRecord(XLogRecGetInfo(record), xlrec,
&parsed);
if (info == XLOG_XACT_COMMIT)
{
Assert(!TransactionIdIsValid(parsed.twophase_xid));
ParseCommitRecord(XLogRecGetInfo(record), xlrec, &parsed);
xact_redo_commit(&parsed, XLogRecGetXid(record),
record->EndRecPtr, XLogRecGetOrigin(record));
}
else
else if (info == XLOG_XACT_COMMIT_PREPARED)
{
Assert(TransactionIdIsValid(parsed.twophase_xid));
xl_xact_commit *xlrec = (xl_xact_commit *) XLogRecGetData(record);
xl_xact_parsed_commit parsed;
ParseCommitRecord(XLogRecGetInfo(record), xlrec, &parsed);
xact_redo_commit(&parsed, parsed.twophase_xid,
record->EndRecPtr, XLogRecGetOrigin(record));
/* Delete TwoPhaseState gxact entry and/or 2PC file. */
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
PrepareRedoRemove(parsed.twophase_xid, false);
LWLockRelease(TwoPhaseStateLock);
}
}
else if (info == XLOG_XACT_ABORT || info == XLOG_XACT_ABORT_PREPARED)
else if (info == XLOG_XACT_ABORT)
{
xl_xact_abort *xlrec = (xl_xact_abort *) XLogRecGetData(record);
xl_xact_parsed_abort parsed;
ParseAbortRecord(XLogRecGetInfo(record), xlrec,
&parsed);
if (info == XLOG_XACT_ABORT)
{
Assert(!TransactionIdIsValid(parsed.twophase_xid));
ParseAbortRecord(XLogRecGetInfo(record), xlrec, &parsed);
xact_redo_abort(&parsed, XLogRecGetXid(record));
}
else
else if (info == XLOG_XACT_ABORT_PREPARED)
{
Assert(TransactionIdIsValid(parsed.twophase_xid));
xl_xact_abort *xlrec = (xl_xact_abort *) XLogRecGetData(record);
xl_xact_parsed_abort parsed;
ParseAbortRecord(XLogRecGetInfo(record), xlrec, &parsed);
xact_redo_abort(&parsed, parsed.twophase_xid);
/* Delete TwoPhaseState gxact entry and/or 2PC file. */
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
PrepareRedoRemove(parsed.twophase_xid, false);
}
LWLockRelease(TwoPhaseStateLock);
}
else if (info == XLOG_XACT_PREPARE)
{
......@@ -5650,9 +5652,11 @@ xact_redo(XLogReaderState *record)
* Store xid and start/end pointers of the WAL record in TwoPhaseState
* gxact entry.
*/
LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
PrepareRedoAdd(XLogRecGetData(record),
record->ReadRecPtr,
record->EndRecPtr);
LWLockRelease(TwoPhaseStateLock);
}
else if (info == XLOG_XACT_ASSIGNMENT)
{
......
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