omap remove_rid might not find entry

Client recovery in the server doesn't add the omap rid for all the
clients that it's waiting for.  It only adds the rid as they connect.  A
client whose recovery timeout expires and is evicted will try to have
its omap rid removed without being added.

Today this triggers a warning and returns an error from a time when the
omap rid lifecycle was more rigid.  Now that it's being called by the
server's reclaim_rid, along with a bunch of other functions that succeed
if called for non-existant clients, let's have the omap remove_rid do
the same.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/omap.c

@@ -485,6 +485,10 @@ static int remove_rid_from_reqs(struct omap_info *ominf, u64 rid, u64 *resp_rid,
  * response if it was the last rid waiting for a response.
  *
  * If this returns an error then the server will shut down.
+ *
+ * This can be called multiple times by different servers if there are
+ * errors reclaiming an evicted mount, so we allow asking to remove a
+ * rid that hasn't been added.
  */
 int scoutfs_omap_remove_rid(struct super_block *sb, u64 rid)
 {
@@ -495,21 +499,20 @@ int scoutfs_omap_remove_rid(struct super_block *sb, u64 rid)
 	u64 resp_id = 0;
 	int ret;
 
-	map = kmalloc(sizeof(struct scoutfs_open_ino_map), GFP_NOFS);
-	if (!map) {
-		ret = -ENOMEM;
-		goto out;
-	}
-
 	spin_lock(&ominf->lock);
 	entry = find_rid(&ominf->rids, rid);
 	if (entry)
 		free_rid(&ominf->rids, entry);
 	spin_unlock(&ominf->lock);
 
-	/* the server really shouldn't be removing a rid it never added */
-	if (WARN_ON_ONCE(!entry)) {
-		ret = -ENOENT;
+	if (!entry) {
+		ret = 0;
+		goto out;
+	}
+
+	map = kmalloc(sizeof(struct scoutfs_open_ino_map), GFP_NOFS);
+	if (!map) {
+		ret = -ENOMEM;
 		goto out;
 	}