4 files changed, 52 insertions, 18 deletions
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 286dd3f7551..43edaf5d873 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -116,6 +116,8 @@ static MemoryContext MdCxt;		/* context for all MdfdVec objects */
  * mdnblocks().
  */
 #define EXTENSION_DONT_CHECK_SIZE	(1 << 4)
+/* don't try to open a segment, if not already open */
+#define EXTENSION_DONT_OPEN			(1 << 5)
 
 
 /* local routines */
@@ -551,12 +553,6 @@ mdclose(SMgrRelation reln, ForkNumber forknum)
 	}
 }
 
-void
-mdrelease(void)
-{
-	closeAllVfds();
-}
-
 /*
  *	mdprefetch() -- Initiate asynchronous read of the specified block of a relation
  */
@@ -605,11 +601,14 @@ mdwriteback(SMgrRelation reln, ForkNumber forknum,
 					segnum_end;
 
 		v = _mdfd_getseg(reln, forknum, blocknum, true /* not used */ ,
-						 EXTENSION_RETURN_NULL);
+						 EXTENSION_DONT_OPEN);
 
 		/*
 		 * We might be flushing buffers of already removed relations, that's
-		 * ok, just ignore that case.
+		 * ok, just ignore that case.  If the segment file wasn't open already
+		 * (ie from a recent mdwrite()), then we don't want to re-open it, to
+		 * avoid a race with PROCSIGNAL_BARRIER_SMGRRELEASE that might leave
+		 * us with a descriptor to a file that is about to be unlinked.
 		 */
 		if (!v)
 			return;
@@ -1202,7 +1201,8 @@ _mdfd_getseg(SMgrRelation reln, ForkNumber forknum, BlockNumber blkno,
 
 	/* some way to handle non-existent segments needs to be specified */
 	Assert(behavior &
-		   (EXTENSION_FAIL | EXTENSION_CREATE | EXTENSION_RETURN_NULL));
+		   (EXTENSION_FAIL | EXTENSION_CREATE | EXTENSION_RETURN_NULL |
+			EXTENSION_DONT_OPEN));
 
 	targetseg = blkno / ((BlockNumber) RELSEG_SIZE);
 
@@ -1213,6 +1213,10 @@ _mdfd_getseg(SMgrRelation reln, ForkNumber forknum, BlockNumber blkno,
 		return v;
 	}
 
+	/* The caller only wants the segment if we already had it open. */
+	if (behavior & EXTENSION_DONT_OPEN)
+		return NULL;
+
 	/*
 	 * The target segment is not yet open. Iterate over all the segments
 	 * between the last opened and the target segment. This way missing
diff --git a/src/backend/storage/smgr/smgr.c b/src/backend/storage/smgr/smgr.c
index 2c7a2b28572..a477f70f0e3 100644
--- a/src/backend/storage/smgr/smgr.c
+++ b/src/backend/storage/smgr/smgr.c
@@ -41,7 +41,6 @@ typedef struct f_smgr
 {
 	void		(*smgr_init) (void);	/* may be NULL */
 	void		(*smgr_shutdown) (void);	/* may be NULL */
-	void		(*smgr_release) (void); /* may be NULL */
 	void		(*smgr_open) (SMgrRelation reln);
 	void		(*smgr_close) (SMgrRelation reln, ForkNumber forknum);
 	void		(*smgr_create) (SMgrRelation reln, ForkNumber forknum,
@@ -70,7 +69,6 @@ static const f_smgr smgrsw[] = {
 	{
 		.smgr_init = mdinit,
 		.smgr_shutdown = NULL,
-		.smgr_release = mdrelease,
 		.smgr_open = mdopen,
 		.smgr_close = mdclose,
 		.smgr_create = mdcreate,
@@ -282,6 +280,42 @@ smgrclose(SMgrRelation reln)
 }
 
 /*
+ *	smgrrelease() -- Release all resources used by this object.
+ *
+ *	The object remains valid.
+ */
+void
+smgrrelease(SMgrRelation reln)
+{
+	for (ForkNumber forknum = 0; forknum <= MAX_FORKNUM; forknum++)
+	{
+		smgrsw[reln->smgr_which].smgr_close(reln, forknum);
+		reln->smgr_cached_nblocks[forknum] = InvalidBlockNumber;
+	}
+}
+
+/*
+ *	smgrreleaseall() -- Release resources used by all objects.
+ *
+ *	This is called for PROCSIGNAL_BARRIER_SMGRRELEASE.
+ */
+void
+smgrreleaseall(void)
+{
+	HASH_SEQ_STATUS status;
+	SMgrRelation reln;
+
+	/* Nothing to do if hashtable not set up */
+	if (SMgrRelationHash == NULL)
+		return;
+
+	hash_seq_init(&status, SMgrRelationHash);
+
+	while ((reln = (SMgrRelation) hash_seq_search(&status)) != NULL)
+		smgrrelease(reln);
+}
+
+/*
  *	smgrcloseall() -- Close all existing SMgrRelation objects.
  */
 void
@@ -698,11 +732,6 @@ AtEOXact_SMgr(void)
 bool
 ProcessBarrierSmgrRelease(void)
 {
-	for (int i = 0; i < NSmgr; i++)
-	{
-		if (smgrsw[i].smgr_release)
-			smgrsw[i].smgr_release();
-	}
-
+	smgrreleaseall();
 	return true;
 }
diff --git a/src/include/storage/md.h b/src/include/storage/md.h
index 6e46d8d96a7..ffffa40db71 100644
--- a/src/include/storage/md.h
+++ b/src/include/storage/md.h
@@ -23,7 +23,6 @@
 extern void mdinit(void);
 extern void mdopen(SMgrRelation reln);
 extern void mdclose(SMgrRelation reln, ForkNumber forknum);
-extern void mdrelease(void);
 extern void mdcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo);
 extern bool mdexists(SMgrRelation reln, ForkNumber forknum);
 extern void mdunlink(RelFileNodeBackend rnode, ForkNumber forknum, bool isRedo);
diff --git a/src/include/storage/smgr.h b/src/include/storage/smgr.h
index 8e3ef92cda1..6b63c60fbd9 100644
--- a/src/include/storage/smgr.h
+++ b/src/include/storage/smgr.h
@@ -85,6 +85,8 @@ extern void smgrclearowner(SMgrRelation *owner, SMgrRelation reln);
 extern void smgrclose(SMgrRelation reln);
 extern void smgrcloseall(void);
 extern void smgrclosenode(RelFileNodeBackend rnode);
+extern void smgrrelease(SMgrRelation reln);
+extern void smgrreleaseall(void);
 extern void smgrcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo);
 extern void smgrdosyncall(SMgrRelation *rels, int nrels);
 extern void smgrdounlinkall(SMgrRelation *rels, int nrels, bool isRedo);