When SaveSlotToPath() is called with elevel=LOG, the early exits don't
release the slot's io_in_progress_lock. Fix attached.
This could result in a walsender being stuck on the lock forever. A
possible way to get into this situation is if the offending code paths
are triggered in a low disk space situation. (This is how it was found;
maybe there are other ways.)
Pavan Deolasee and Craig Ringer worked on this issue. I'm forwarding it
on their behalf.
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
From b33a856c68e1c48c8663a760f79b2b3d3bf0088c Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pe...@eisentraut.org>
Date: Wed, 18 Mar 2020 16:24:59 +0100
Subject: [PATCH] Drop slot's LWLock before returning from SaveSlotToPath()
When SaveSlotToPath() is called with elevel=LOG, the early exits didn't
release the slot's io_in_progress_lock.
This could result in a walsender being stuck on the lock forever. A
possible way to get into this situation is if the offending code paths
are triggered in a low disk space situation.
Author: Pavan Deolasee <pavan.deola...@2ndquadrant.com>
Reported-by: Craig Ringer <cr...@2ndquadrant.com>
---
src/backend/replication/slot.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 1cec53d748..1bff2d6185 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1256,6 +1256,13 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir,
int elevel)
fd = OpenTransientFile(tmppath, O_CREAT | O_EXCL | O_WRONLY |
PG_BINARY);
if (fd < 0)
{
+ /*
+ * If not an ERROR, then release the lock before returning the
control
+ * back to the caller. In case of an ERROR, the error recovery
path
+ * should automatically release the lock, but no harm in
explicitly
+ * releaseing even in that case.
+ */
+ LWLockRelease(&slot->io_in_progress_lock);
ereport(elevel,
(errcode_for_file_access(),
errmsg("could not create file \"%s\": %m",
@@ -1287,6 +1294,7 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir,
int elevel)
pgstat_report_wait_end();
CloseTransientFile(fd);
+ LWLockRelease(&slot->io_in_progress_lock);
/* if write didn't set errno, assume problem is no disk space */
errno = save_errno ? save_errno : ENOSPC;
@@ -1306,6 +1314,7 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir,
int elevel)
pgstat_report_wait_end();
CloseTransientFile(fd);
+ LWLockRelease(&slot->io_in_progress_lock);
errno = save_errno;
ereport(elevel,
(errcode_for_file_access(),
@@ -1317,6 +1326,7 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir,
int elevel)
if (CloseTransientFile(fd) != 0)
{
+ LWLockRelease(&slot->io_in_progress_lock);
ereport(elevel,
(errcode_for_file_access(),
errmsg("could not close file \"%s\": %m",
@@ -1327,6 +1337,7 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir,
int elevel)
/* rename to permanent file, fsync file and directory */
if (rename(tmppath, path) != 0)
{
+ LWLockRelease(&slot->io_in_progress_lock);
ereport(elevel,
(errcode_for_file_access(),
errmsg("could not rename file \"%s\" to
\"%s\": %m",
--
2.25.0
