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Don't be so trusting that shm_toc_lookup() will always succeed.

Browse Source 
Given the possibility of race conditions and so on, it seems entirely
unsafe to just assume that shm_toc_lookup() always finds the key it's
looking for --- but that was exactly what all but one call site were
doing.  To fix, add a "bool noError" argument, similarly to what we
have in many other functions, and throw an error on an unexpected
lookup failure.  Remove now-redundant Asserts that a rather random
subset of call sites had.

I doubt this will throw any light on buildfarm member lorikeet's
recent failures, because if an unnoticed lookup failure were involved,
you'd kind of expect a null-pointer-dereference crash rather than the
observed symptom.  But you never know ... and this is better coding
practice even if it never catches anything.

Discussion: https://postgr.es/m/9697.1496675981@sss.pgh.pa.us
This commit is contained in:
Tom Lane 2017-06-05 12:05:42 -04:00
parent af51fea039
commit d466335064
11 changed files with 39 additions and 38 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
src/backend/access/transam/parallel.c
View File

@ -392,12 +392,12 @@ ReinitializeParallelDSM(ParallelContext *pcxt)
}
/* Reset a few bits of fixed parallel state to a clean state. */
fps = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_FIXED);
fps = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_FIXED, false);
fps->last_xlog_end = 0;
/* Recreate error queues. */
error_queue_space =
shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE);
shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, false);
for (i = 0; i < pcxt->nworkers; ++i)
{
char *start;
@ -536,7 +536,7 @@ WaitForParallelWorkersToFinish(ParallelContext *pcxt)
{
FixedParallelState *fps;
fps = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_FIXED);
fps = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_FIXED, false);
if (fps->last_xlog_end > XactLastRecEnd)
XactLastRecEnd = fps->last_xlog_end;
}
@ -973,8 +973,7 @@ ParallelWorkerMain(Datum main_arg)
errmsg("invalid magic number in dynamic shared memory segment")));
/* Look up fixed parallel state. */
fps = shm_toc_lookup(toc, PARALLEL_KEY_FIXED);
Assert(fps != NULL);
fps = shm_toc_lookup(toc, PARALLEL_KEY_FIXED, false);
MyFixedParallelState = fps;
/*
@ -983,7 +982,7 @@ ParallelWorkerMain(Datum main_arg)
* errors that happen here will not be reported back to the process that
* requested that this worker be launched.
*/
error_queue_space = shm_toc_lookup(toc, PARALLEL_KEY_ERROR_QUEUE);
error_queue_space = shm_toc_lookup(toc, PARALLEL_KEY_ERROR_QUEUE, false);
mq = (shm_mq *) (error_queue_space +
ParallelWorkerNumber * PARALLEL_ERROR_QUEUE_SIZE);
shm_mq_set_sender(mq, MyProc);
@ -1027,8 +1026,7 @@ ParallelWorkerMain(Datum main_arg)
* this before restoring GUCs, because the libraries might define custom
* variables.
*/
libraryspace = shm_toc_lookup(toc, PARALLEL_KEY_LIBRARY);
Assert(libraryspace != NULL);
libraryspace = shm_toc_lookup(toc, PARALLEL_KEY_LIBRARY, false);
RestoreLibraryState(libraryspace);
/*
@ -1036,8 +1034,7 @@ ParallelWorkerMain(Datum main_arg)
* loading an additional library, though most likely the entry point is in
* the core backend or in a library we just loaded.
*/
entrypointstate = shm_toc_lookup(toc, PARALLEL_KEY_ENTRYPOINT);
Assert(entrypointstate != NULL);
entrypointstate = shm_toc_lookup(toc, PARALLEL_KEY_ENTRYPOINT, false);
library_name = entrypointstate;
function_name = entrypointstate + strlen(library_name) + 1;
@ -1054,30 +1051,26 @@ ParallelWorkerMain(Datum main_arg)
SetClientEncoding(GetDatabaseEncoding());
/* Restore GUC values from launching backend. */
gucspace = shm_toc_lookup(toc, PARALLEL_KEY_GUC);
Assert(gucspace != NULL);
gucspace = shm_toc_lookup(toc, PARALLEL_KEY_GUC, false);
StartTransactionCommand();
RestoreGUCState(gucspace);
CommitTransactionCommand();
/* Crank up a transaction state appropriate to a parallel worker. */
tstatespace = shm_toc_lookup(toc, PARALLEL_KEY_TRANSACTION_STATE);
tstatespace = shm_toc_lookup(toc, PARALLEL_KEY_TRANSACTION_STATE, false);
StartParallelWorkerTransaction(tstatespace);
/* Restore combo CID state. */
combocidspace = shm_toc_lookup(toc, PARALLEL_KEY_COMBO_CID);
Assert(combocidspace != NULL);
combocidspace = shm_toc_lookup(toc, PARALLEL_KEY_COMBO_CID, false);
RestoreComboCIDState(combocidspace);
/* Restore transaction snapshot. */
tsnapspace = shm_toc_lookup(toc, PARALLEL_KEY_TRANSACTION_SNAPSHOT);
Assert(tsnapspace != NULL);
tsnapspace = shm_toc_lookup(toc, PARALLEL_KEY_TRANSACTION_SNAPSHOT, false);
RestoreTransactionSnapshot(RestoreSnapshot(tsnapspace),
fps->parallel_master_pgproc);
/* Restore active snapshot. */
asnapspace = shm_toc_lookup(toc, PARALLEL_KEY_ACTIVE_SNAPSHOT);
Assert(asnapspace != NULL);
asnapspace = shm_toc_lookup(toc, PARALLEL_KEY_ACTIVE_SNAPSHOT, false);
PushActiveSnapshot(RestoreSnapshot(asnapspace));
/*

16
src/backend/executor/execParallel.c
View File

@ -341,7 +341,7 @@ ExecParallelSetupTupleQueues(ParallelContext *pcxt, bool reinitialize)
mul_size(PARALLEL_TUPLE_QUEUE_SIZE,
pcxt->nworkers));
else
tqueuespace = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_TUPLE_QUEUE);
tqueuespace = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_TUPLE_QUEUE, false);
/* Create the queues, and become the receiver for each. */
for (i = 0; i < pcxt->nworkers; ++i)
@ -684,7 +684,7 @@ ExecParallelGetReceiver(dsm_segment *seg, shm_toc *toc)
char *mqspace;
shm_mq *mq;
mqspace = shm_toc_lookup(toc, PARALLEL_KEY_TUPLE_QUEUE);
mqspace = shm_toc_lookup(toc, PARALLEL_KEY_TUPLE_QUEUE, false);
mqspace += ParallelWorkerNumber * PARALLEL_TUPLE_QUEUE_SIZE;
mq = (shm_mq *) mqspace;
shm_mq_set_sender(mq, MyProc);
@ -705,14 +705,14 @@ ExecParallelGetQueryDesc(shm_toc *toc, DestReceiver *receiver,
char *queryString;
/* Get the query string from shared memory */
queryString = shm_toc_lookup(toc, PARALLEL_KEY_QUERY_TEXT);
queryString = shm_toc_lookup(toc, PARALLEL_KEY_QUERY_TEXT, false);
/* Reconstruct leader-supplied PlannedStmt. */
pstmtspace = shm_toc_lookup(toc, PARALLEL_KEY_PLANNEDSTMT);
pstmtspace = shm_toc_lookup(toc, PARALLEL_KEY_PLANNEDSTMT, false);
pstmt = (PlannedStmt *) stringToNode(pstmtspace);
/* Reconstruct ParamListInfo. */
paramspace = shm_toc_lookup(toc, PARALLEL_KEY_PARAMS);
paramspace = shm_toc_lookup(toc, PARALLEL_KEY_PARAMS, false);
paramLI = RestoreParamList(&paramspace);
/*
@ -843,7 +843,7 @@ ParallelQueryMain(dsm_segment *seg, shm_toc *toc)
/* Set up DestReceiver, SharedExecutorInstrumentation, and QueryDesc. */
receiver = ExecParallelGetReceiver(seg, toc);
instrumentation = shm_toc_lookup(toc, PARALLEL_KEY_INSTRUMENTATION);
instrumentation = shm_toc_lookup(toc, PARALLEL_KEY_INSTRUMENTATION, true);
if (instrumentation != NULL)
instrument_options = instrumentation->instrument_options;
queryDesc = ExecParallelGetQueryDesc(toc, receiver, instrument_options);
@ -858,7 +858,7 @@ ParallelQueryMain(dsm_segment *seg, shm_toc *toc)
InstrStartParallelQuery();
/* Attach to the dynamic shared memory area. */
area_space = shm_toc_lookup(toc, PARALLEL_KEY_DSA);
area_space = shm_toc_lookup(toc, PARALLEL_KEY_DSA, false);
area = dsa_attach_in_place(area_space, seg);
/* Start up the executor */
@ -875,7 +875,7 @@ ParallelQueryMain(dsm_segment *seg, shm_toc *toc)
ExecutorFinish(queryDesc);
/* Report buffer usage during parallel execution. */
buffer_usage = shm_toc_lookup(toc, PARALLEL_KEY_BUFFER_USAGE);
buffer_usage = shm_toc_lookup(toc, PARALLEL_KEY_BUFFER_USAGE, false);
InstrEndParallelQuery(&buffer_usage[ParallelWorkerNumber]);
/* Report instrumentation data if any instrumentation options are set. */

2
src/backend/executor/nodeBitmapHeapscan.c
View File

@ -1005,7 +1005,7 @@ ExecBitmapHeapInitializeWorker(BitmapHeapScanState *node, shm_toc *toc)
ParallelBitmapHeapState *pstate;
Snapshot snapshot;
pstate = shm_toc_lookup(toc, node->ss.ps.plan->plan_node_id);
pstate = shm_toc_lookup(toc, node->ss.ps.plan->plan_node_id, false);
node->pstate = pstate;
snapshot = RestoreSnapshot(pstate->phs_snapshot_data);

2
src/backend/executor/nodeCustom.c
View File

@ -194,7 +194,7 @@ ExecCustomScanInitializeWorker(CustomScanState *node, shm_toc *toc)
int plan_node_id = node->ss.ps.plan->plan_node_id;
void *coordinate;
coordinate = shm_toc_lookup(toc, plan_node_id);
coordinate = shm_toc_lookup(toc, plan_node_id, false);
methods->InitializeWorkerCustomScan(node, toc, coordinate);
}
}

2
src/backend/executor/nodeForeignscan.c
View File

@ -344,7 +344,7 @@ ExecForeignScanInitializeWorker(ForeignScanState *node, shm_toc *toc)
int plan_node_id = node->ss.ps.plan->plan_node_id;
void *coordinate;
coordinate = shm_toc_lookup(toc, plan_node_id);
coordinate = shm_toc_lookup(toc, plan_node_id, false);
fdwroutine->InitializeWorkerForeignScan(node, toc, coordinate);
}
}

2
src/backend/executor/nodeIndexonlyscan.c
View File

@ -676,7 +676,7 @@ ExecIndexOnlyScanInitializeWorker(IndexOnlyScanState *node, shm_toc *toc)
{
ParallelIndexScanDesc piscan;
piscan = shm_toc_lookup(toc, node->ss.ps.plan->plan_node_id);
piscan = shm_toc_lookup(toc, node->ss.ps.plan->plan_node_id, false);
node->ioss_ScanDesc =
index_beginscan_parallel(node->ss.ss_currentRelation,
node->ioss_RelationDesc,

2
src/backend/executor/nodeIndexscan.c
View File

@ -1714,7 +1714,7 @@ ExecIndexScanInitializeWorker(IndexScanState *node, shm_toc *toc)
{
ParallelIndexScanDesc piscan;
piscan = shm_toc_lookup(toc, node->ss.ps.plan->plan_node_id);
piscan = shm_toc_lookup(toc, node->ss.ps.plan->plan_node_id, false);
node->iss_ScanDesc =
index_beginscan_parallel(node->ss.ss_currentRelation,
node->iss_RelationDesc,

2
src/backend/executor/nodeSeqscan.c
View File

@ -332,7 +332,7 @@ ExecSeqScanInitializeWorker(SeqScanState *node, shm_toc *toc)
{
ParallelHeapScanDesc pscan;
pscan = shm_toc_lookup(toc, node->ss.ps.plan->plan_node_id);
pscan = shm_toc_lookup(toc, node->ss.ps.plan->plan_node_id, false);
node->ss.ss_currentScanDesc =
heap_beginscan_parallel(node->ss.ss_currentRelation, pscan);
}

10
src/backend/storage/ipc/shm_toc.c
View File

@ -208,6 +208,9 @@ shm_toc_insert(shm_toc *toc, uint64 key, void *address)
/*
* Look up a TOC entry.
*
* If the key is not found, returns NULL if noError is true, otherwise
* throws elog(ERROR).
*
* Unlike the other functions in this file, this operation acquires no lock;
* it uses only barriers. It probably wouldn't hurt concurrency very much even
* if it did get a lock, but since it's reasonably likely that a group of
@ -215,7 +218,7 @@ shm_toc_insert(shm_toc *toc, uint64 key, void *address)
* right around the same time, there seems to be some value in avoiding it.
*/
void *
shm_toc_lookup(shm_toc *toc, uint64 key)
shm_toc_lookup(shm_toc *toc, uint64 key, bool noError)
{
uint64 nentry;
uint64 i;
@ -226,10 +229,15 @@ shm_toc_lookup(shm_toc *toc, uint64 key)
/* Now search for a matching entry. */
for (i = 0; i < nentry; ++i)
{
if (toc->toc_entry[i].key == key)
return ((char *) toc) + toc->toc_entry[i].offset;
}
/* No matching entry was found. */
if (!noError)
elog(ERROR, "could not find key " UINT64_FORMAT " in shm TOC at %p",
key, toc);
return NULL;
}

2
src/include/storage/shm_toc.h
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@ -32,7 +32,7 @@ extern shm_toc *shm_toc_attach(uint64 magic, void *address);
extern void *shm_toc_allocate(shm_toc *toc, Size nbytes);
extern Size shm_toc_freespace(shm_toc *toc);
extern void shm_toc_insert(shm_toc *toc, uint64 key, void *address);
extern void *shm_toc_lookup(shm_toc *toc, uint64 key);
extern void *shm_toc_lookup(shm_toc *toc, uint64 key, bool noError);
/*
* Tools for estimating how large a chunk of shared memory will be needed

6
src/test/modules/test_shm_mq/worker.c
View File

@ -95,7 +95,7 @@ test_shm_mq_main(Datum main_arg)
* find it. Our worker number gives our identity: there may be just one
* worker involved in this parallel operation, or there may be many.
*/
hdr = shm_toc_lookup(toc, 0);
hdr = shm_toc_lookup(toc, 0, false);
SpinLockAcquire(&hdr->mutex);
myworkernumber = ++hdr->workers_attached;
SpinLockRelease(&hdr->mutex);
@ -158,10 +158,10 @@ attach_to_queues(dsm_segment *seg, shm_toc *toc, int myworkernumber,
shm_mq *inq;
shm_mq *outq;
inq = shm_toc_lookup(toc, myworkernumber);
inq = shm_toc_lookup(toc, myworkernumber, false);
shm_mq_set_receiver(inq, MyProc);
*inqhp = shm_mq_attach(inq, seg, NULL);
outq = shm_toc_lookup(toc, myworkernumber + 1);
outq = shm_toc_lookup(toc, myworkernumber + 1, false);
shm_mq_set_sender(outq, MyProc);
*outqhp = shm_mq_attach(outq, seg, NULL);
}