postgres.git / summary / log / commit / refs

commit    bef2d627f30c0d854d02dc860b0d54fa3309d4ee
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Fri Aug 26 19:04:05 2016 +0000
First released in: 10.0, 9.5.5, 9.6.0

    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 ec6e1c5e6dc..949bfb8b3e6 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();
 }
 


[parent: 42ebdc8129f0]