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.deolasee@2ndquadrant.com>
Reported-by: Craig Ringer <craig@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/flat/56a138c5-de61-f553-7e8f-6789296de785%402ndquadrant.com

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9a6cde09bc31def45e24356e20c1e1a6f7f0af15..14fc04df09cb7369799c68f30a250d82e67fc456 100644 (file)
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1010,6 +1010,12 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel)
                                                   S_IRUSR | S_IWUSR);
        if (fd < 0)
        {
+               /*
+                * If not an ERROR, then release the lock before returning.  In case
+                * of an ERROR, the error recovery path automatically releases the
+                * lock, but no harm in explicitly releasing even in that case.
+                */
+               LWLockRelease(slot->io_in_progress_lock);
                ereport(elevel,
                                (errcode_for_file_access(),
                                 errmsg("could not create file \"%s\": %m",
@@ -1039,6 +1045,7 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel)
                int                     save_errno = errno;
 
                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;
@@ -1055,6 +1062,7 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel)
                int                     save_errno = errno;
 
                CloseTransientFile(fd);
+               LWLockRelease(slot->io_in_progress_lock);
                errno = save_errno;
                ereport(elevel,
                                (errcode_for_file_access(),
@@ -1068,6 +1076,7 @@ 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",