From bef2d627f30c0d854d02dc860b0d54fa3309d4ee Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 26 Aug 2016 15:04:05 -0400 Subject: [PATCH] Fix potential memory leakage from HandleParallelMessages(). HandleParallelMessages leaked memory into the caller's context. Since it's called from ProcessInterrupts, there is basically zero certainty as to what CurrentMemoryContext is, which means we could be leaking into long-lived contexts. Over the processing of many worker messages that would grow to be a problem. Things could be even worse than just a leak, if we happened to service the interrupt while ErrorContext is current: elog.c thinks it can reset that on its own whim, possibly yanking storage out from under HandleParallelMessages. Give HandleParallelMessages its own dedicated context instead, which we can reset during each call to ensure there's no accumulation of wasted memory. Discussion: <16610.1472222135@sss.pgh.pa.us> --- src/backend/access/transam/parallel.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c index ec6e1c5e6d..949bfb8b3e 100644 --- a/src/backend/access/transam/parallel.c +++ b/src/backend/access/transam/parallel.c @@ -702,6 +702,9 @@ void HandleParallelMessages(void) { dlist_iter iter; + MemoryContext oldcontext; + + static MemoryContext hpm_context = NULL; /* * This is invoked from ProcessInterrupts(), and since some of the @@ -712,6 +715,23 @@ HandleParallelMessages(void) */ HOLD_INTERRUPTS(); + /* + * Moreover, CurrentMemoryContext might be pointing almost anywhere. We + * don't want to risk leaking data into long-lived contexts, so let's do + * our work here in a private context that we can reset on each use. + */ + if (hpm_context == NULL) /* first time through? */ + hpm_context = AllocSetContextCreate(TopMemoryContext, + "HandleParallelMessages context", + ALLOCSET_DEFAULT_MINSIZE, + ALLOCSET_DEFAULT_INITSIZE, + ALLOCSET_DEFAULT_MAXSIZE); + else + MemoryContextReset(hpm_context); + + oldcontext = MemoryContextSwitchTo(hpm_context); + + /* OK to process messages. Reset the flag saying there are more to do. */ ParallelMessagePending = false; dlist_foreach(iter, &pcxt_list) @@ -758,6 +778,11 @@ HandleParallelMessages(void) } } + MemoryContextSwitchTo(oldcontext); + + /* Might as well clear the context on our way out */ + MemoryContextReset(hpm_context); + RESUME_INTERRUPTS(); }