Save errno across LWLockRelease() calls

petere · petere · commit 038c9bbe9b61 · 2020-04-05T10:04:13.000+02:00
Fixup for "Drop slot's LWLock before returning from SaveSlotToPath()"

Reported-by: Michael Paquier &lt;michael@paquier.xyz&gt;
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
@@ -1254,9 +1254,13 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel)
 		/*
 		 * 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.
+		 * lock, but no harm in explicitly releasing even in that case.  Note
+		 * that LWLockRelease() could affect errno.
 		 */
+		int			save_errno = errno;
+
 		LWLockRelease(&slot->io_in_progress_lock);
+		errno = save_errno;
 		ereport(elevel,
 				(errcode_for_file_access(),
 				 errmsg("could not create file \"%s\": %m",
@@ -1323,7 +1327,10 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel)
 	/* rename to permanent file, fsync file and directory */
 	if (rename(tmppath, path) != 0)
 	{
+		int			save_errno = errno;
+
 		LWLockRelease(&slot->io_in_progress_lock);
+		errno = save_errno;
 		ereport(elevel,
 				(errcode_for_file_access(),
 				 errmsg("could not rename file \"%s\" to \"%s\": %m",
