0001-Fix-thinko-in-handling-of-corrupted-DSM-control-area.patch

From b5f7903b97ab9d0539630bab8805fcbcdcef793d Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@enterprisedb.com>
Date: Thu, 18 Oct 2018 10:48:18 +1300
Subject: [PATCH] Fix thinko in handling of corrupted DSM control area.

If dsm_cleanup_using_control_segment() or dsm_postmaster_shutdown()
determine that the DSM control segment is corrupted, they should still
destroy it, otherwise it is leaked.  This fixes an assertion failure
in dsm_postmaster_startup().

Reported by build-farm animal peripatus.  The root cause of the
corrupted segment in that case is not yet known, but that's another
matter.

Author: Thomas Munro
Diagnosed-by: Tom Lane
Discussion: https://postgr.es/m/6153.1539806400%40sss.pgh.pa.us
---
 src/backend/storage/ipc/dsm.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c
index 9629f22f7af..f24bf2e74a1 100644
--- a/src/backend/storage/ipc/dsm.c
+++ b/src/backend/storage/ipc/dsm.c
@@ -138,8 +138,7 @@ static void *dsm_control_impl_private = NULL;
 /*
  * Start up the dynamic shared memory system.
  *
- * This is called just once during each cluster lifetime, at postmaster
- * startup time.
+ * This is called at postmaster startup time, and again during crash restarts.
  */
 void
 dsm_postmaster_startup(PGShmemHeader *shim)
@@ -227,21 +226,19 @@ dsm_cleanup_using_control_segment(dsm_handle old_control_handle)
 
 	/*
 	 * We've managed to reattach it, but the contents might not be sane. If
-	 * they aren't, we disregard the segment after all.
+	 * they aren't, we disregard the contents of the segment after all.
 	 */
 	old_control = (dsm_control_header *) mapped_address;
 	if (!dsm_control_segment_sane(old_control, mapped_size))
 	{
 		dsm_impl_op(DSM_OP_DETACH, old_control_handle, 0, &impl_private,
 					&mapped_address, &mapped_size, LOG);
-		return;
+		nitems = 0;
 	}
+	else
+		nitems = old_control->nitems;
 
-	/*
-	 * OK, the control segment looks basically valid, so we can use it to get
-	 * a list of segments that need to be removed.
-	 */
-	nitems = old_control->nitems;
+	/* Get a list of segments that need to be removed. */
 	for (i = 0; i < nitems; ++i)
 	{
 		dsm_handle	handle;
@@ -336,13 +333,14 @@ dsm_postmaster_shutdown(int code, Datum arg)
 	 * stray shared memory segments, but there's not much we can do about that
 	 * if the metadata is gone.
 	 */
-	nitems = dsm_control->nitems;
 	if (!dsm_control_segment_sane(dsm_control, dsm_control_mapped_size))
 	{
 		ereport(LOG,
 				(errmsg("dynamic shared memory control segment is corrupt")));
-		return;
+		nitems = 0;
 	}
+	else
+		nitems = dsm_control->nitems;
 
 	/* Remove any remaining segments. */
 	for (i = 0; i < nitems; ++i)
-- 
2.17.1 (Apple Git-112)