* [RFC PATCH] notifier: Return non-null when callback already registered
@ 2021-05-20 20:20 Borislav Petkov
2021-05-21 11:11 ` Peter Zijlstra
0 siblings, 1 reply; 3+ messages in thread
From: Borislav Petkov @ 2021-05-20 20:20 UTC (permalink / raw)
To: X86 ML; +Cc: LKML
From: Borislav Petkov <bp@suse.de>
The notifier registration routine doesn't return a proper error value
when a callback has already been registered, leading people to track
whether that regisration has happened at the call site:
https://lore.kernel.org/amd-gfx/20210512013058.6827-1-mukul.joshi@amd.com/
Which is unnecessary.
Return a non-null to signal that case so that callers can act
accordingly.
Signed-off-by: Borislav Petkov <bp@suse.de>
---
kernel/notifier.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/notifier.c b/kernel/notifier.c
index 1b019cbca594..ff7a3198c5fc 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -25,7 +25,7 @@ static int notifier_chain_register(struct notifier_block **nl,
while ((*nl) != NULL) {
if (unlikely((*nl) == n)) {
WARN(1, "double register detected");
- return 0;
+ return 1;
}
if (n->priority > (*nl)->priority)
break;
@@ -134,7 +134,7 @@ static int notifier_call_chain_robust(struct notifier_block **nl,
*
* Adds a notifier to an atomic notifier chain.
*
- * Currently always returns zero.
+ * Returns 0 on success, !0 on error.
*/
int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
struct notifier_block *n)
@@ -235,7 +235,7 @@ NOKPROBE_SYMBOL(atomic_notifier_call_chain);
* Adds a notifier to a blocking notifier chain.
* Must be called in process context.
*
- * Currently always returns zero.
+ * Returns 0 on success, !0 on error.
*/
int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
struct notifier_block *n)
@@ -354,7 +354,7 @@ EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);
* Adds a notifier to a raw notifier chain.
* All locking must be provided by the caller.
*
- * Currently always returns zero.
+ * Returns 0 on success, !0 on error.
*/
int raw_notifier_chain_register(struct raw_notifier_head *nh,
struct notifier_block *n)
@@ -425,7 +425,7 @@ EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
* Adds a notifier to an SRCU notifier chain.
* Must be called in process context.
*
- * Currently always returns zero.
+ * Returns 0 on success, !0 on error.
*/
int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
struct notifier_block *n)
--
2.29.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [RFC PATCH] notifier: Return non-null when callback already registered
2021-05-20 20:20 [RFC PATCH] notifier: Return non-null when callback already registered Borislav Petkov
@ 2021-05-21 11:11 ` Peter Zijlstra
2021-05-21 14:06 ` Borislav Petkov
0 siblings, 1 reply; 3+ messages in thread
From: Peter Zijlstra @ 2021-05-21 11:11 UTC (permalink / raw)
To: Borislav Petkov; +Cc: X86 ML, LKML
On Thu, May 20, 2021 at 10:20:33PM +0200, Borislav Petkov wrote:
> From: Borislav Petkov <bp@suse.de>
>
> The notifier registration routine doesn't return a proper error value
> when a callback has already been registered, leading people to track
> whether that regisration has happened at the call site:
>
> https://lore.kernel.org/amd-gfx/20210512013058.6827-1-mukul.joshi@amd.com/
>
> Which is unnecessary.
>
> Return a non-null to signal that case so that callers can act
> accordingly.
>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> ---
> kernel/notifier.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/notifier.c b/kernel/notifier.c
> index 1b019cbca594..ff7a3198c5fc 100644
> --- a/kernel/notifier.c
> +++ b/kernel/notifier.c
> @@ -25,7 +25,7 @@ static int notifier_chain_register(struct notifier_block **nl,
> while ((*nl) != NULL) {
> if (unlikely((*nl) == n)) {
> WARN(1, "double register detected");
That should give a big clue^
> - return 0;
> + return 1;
How about -EBUSY here?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [RFC PATCH] notifier: Return non-null when callback already registered
2021-05-21 11:11 ` Peter Zijlstra
@ 2021-05-21 14:06 ` Borislav Petkov
0 siblings, 0 replies; 3+ messages in thread
From: Borislav Petkov @ 2021-05-21 14:06 UTC (permalink / raw)
To: Peter Zijlstra; +Cc: X86 ML, LKML
On Fri, May 21, 2021 at 01:11:42PM +0200, Peter Zijlstra wrote:
> > @@ -25,7 +25,7 @@ static int notifier_chain_register(struct notifier_block **nl,
> > while ((*nl) != NULL) {
> > if (unlikely((*nl) == n)) {
> > WARN(1, "double register detected");
>
> That should give a big clue^
Yah, the big cluebat... Was wondering whether to remove it, actually.
But then I'd need to audit all users whether they handle retval
properly. Sounds like a kernelnewbies project to me...
> > - return 0;
> > + return 1;
>
> How about -EBUSY here?
Yah, anthing but 0.
But if we're gonna return -E things, -EEXIST looks like an even better
fit to me...
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-05-20 20:20 [RFC PATCH] notifier: Return non-null when callback already registered Borislav Petkov
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