notifier: Return an error when a callback has already been registered

Return -EEXIST when a notifier callback has already been registered on a notifier chain. This should avoid any homegrown registration tracking at the callsite like https://lore.kernel.org/amd-gfx/20210512013058.6827-1-mukul.joshi@amd.com for example. This version is an alternative of https://lore.kernel.org/r/20211108101157.15189-1-bp@alien8.de which needed to touch every caller not checking the registration routine's return value.

Borislav Petkov committed 4 years ago

Commit 5abb0651 parent fc74e0a1 file · +8 −7Browse files

Showing the changes to kernel (1 of 1 file). Show all

Unified · Split

kernel/notifier.c+8−7

@@ -20,12 +20,13 @@ BLOCKING_NOTIFIER_HEAD(reboot_notifier_list); · 19 unmodified lines
20	20	*/
21	21
22	22	static int notifier_chain_register(struct notifier_block **nl,
23		− struct notifier_block *n)
	23	+ struct notifier_block *n)
24	24	{
25	25	while ((*nl) != NULL) {
26	26	if (unlikely((*nl) == n)) {
27		− WARN(1, "double register detected");
28		− return 0;
	27	+ WARN(1, "notifier callback %ps already registered",
	28	+ n->notifier_call);
	29	+ return -EEXIST;
29	30	}
30	31	if (n->priority > (*nl)->priority)
31	32	break;
@@ -134,7 +135,7 @@ static int notifier_call_chain_robust(struct notifier_block **nl, · 102 unmodified lines
134	135	*
135	136	* Adds a notifier to an atomic notifier chain.
136	137	*
137		− * Currently always returns zero.
	138	+ * Returns 0 on success, %-EEXIST on error.
138	139	*/
139	140	int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
140	141	struct notifier_block *n)
@@ -216,7 +217,7 @@ NOKPROBE_SYMBOL(atomic_notifier_call_chain); · 75 unmodified lines
216	217	* Adds a notifier to a blocking notifier chain.
217	218	* Must be called in process context.
218	219	*
219		− * Currently always returns zero.
	220	+ * Returns 0 on success, %-EEXIST on error.
220	221	*/
221	222	int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
222	223	struct notifier_block *n)
@@ -335,7 +336,7 @@ EXPORT_SYMBOL_GPL(blocking_notifier_call_chain); · 112 unmodified lines
335	336	* Adds a notifier to a raw notifier chain.
336	337	* All locking must be provided by the caller.
337	338	*
338		− * Currently always returns zero.
	339	+ * Returns 0 on success, %-EEXIST on error.
339	340	*/
340	341	int raw_notifier_chain_register(struct raw_notifier_head *nh,
341	342	struct notifier_block *n)
@@ -406,7 +407,7 @@ EXPORT_SYMBOL_GPL(raw_notifier_call_chain); · 64 unmodified lines
406	407	* Adds a notifier to an SRCU notifier chain.
407	408	* Must be called in process context.
408	409	*
409		− * Currently always returns zero.
	410	+ * Returns 0 on success, %-EEXIST on error.
410	411	*/
411	412	int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
412	413	struct notifier_block *n)