---

yaml
---
r: 359387
b: refs/heads/master
c: 7175c61
h: refs/heads/master
i:
  359385: ba52d9a
  359383: 7e24e06
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 0ffc2a9c8072969253a20821c2c733a2cbb4c7c7
+refs/heads/master: 7175c61cc6b8e701441e79ef048c11ae97293463

trunk/lib/idr.c

@@ -569,6 +569,7 @@ void idr_remove(struct idr *idp, int id)
 	struct idr_layer *p;
 	struct idr_layer *to_free;
 
+	/* see comment in idr_find_slowpath() */
 	if (WARN_ON_ONCE(id < 0))
 		return;
 
@@ -666,6 +667,14 @@ void *idr_find_slowpath(struct idr *idp, int id)
 	int n;
 	struct idr_layer *p;
 
+	/*
+	 * If @id is negative, idr_find() used to ignore the sign bit and
+	 * performed lookup with the rest of bits, which is weird and can
+	 * lead to very obscure bugs.  We're now returning NULL for all
+	 * negative IDs but just in case somebody was depending on the sign
+	 * bit being ignored, let's trigger WARN_ON_ONCE() so that they can
+	 * be detected and fixed.  WARN_ON_ONCE() can later be removed.
+	 */
 	if (WARN_ON_ONCE(id < 0))
 		return NULL;
 
@@ -815,6 +824,7 @@ void *idr_replace(struct idr *idp, void *ptr, int id)
 	int n;
 	struct idr_layer *p, *old_p;
 
+	/* see comment in idr_find_slowpath() */
 	if (WARN_ON_ONCE(id < 0))
 		return ERR_PTR(-EINVAL);