database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-06-16 06:01:02 +03:00
Code Activity

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
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));
/*