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Date: Mon, 8 Nov 2021 11:11:57 +0100
From: Borislav Petkov <bp@...en8.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Arnd Bergmann <arnd@...db.de>,
Ayush Sawal <ayush.sawal@...lsio.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Rohit Maheshwari <rohitm@...lsio.com>,
Steven Rostedt <rostedt@...dmis.org>,
Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
alsa-devel@...a-project.org, bcm-kernel-feedback-list@...adcom.com,
intel-gfx@...ts.freedesktop.org,
intel-gvt-dev@...ts.freedesktop.org, linux-alpha@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
linux-crypto@...r.kernel.org, linux-edac@...r.kernel.org,
linux-fbdev@...r.kernel.org, linux-hyperv@...r.kernel.org,
linux-iio@...r.kernel.org, linux-leds@...r.kernel.org,
linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
linux-pm@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
linux-remoteproc@...r.kernel.org,
linux-renesas-soc@...r.kernel.org, linux-s390@...r.kernel.org,
linux-scsi@...r.kernel.org, linux-sh@...r.kernel.org,
linux-staging@...ts.linux.dev, linux-tegra@...r.kernel.org,
linux-um@...ts.infradead.org, linux-usb@...r.kernel.org,
linux-xtensa@...ux-xtensa.org, netdev@...r.kernel.org,
openipmi-developer@...ts.sourceforge.net, rcu@...r.kernel.org,
sparclinux@...r.kernel.org, x86@...nel.org,
xen-devel@...ts.xenproject.org
Subject: [PATCH v0 42/42] notifier: Return an error when callback is already registered
From: Borislav Petkov <bp@...e.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 registration has happened at the call site:
https://lore.kernel.org/amd-gfx/20210512013058.6827-1-mukul.joshi@amd.com/
Which is unnecessary.
Return -EEXIST to signal that case so that callers can act accordingly.
Enforce callers to check the return value, leading to loud screaming
during build:
arch/x86/kernel/cpu/mce/core.c: In function ‘mce_register_decode_chain’:
arch/x86/kernel/cpu/mce/core.c:167:2: error: ignoring return value of \
‘blocking_notifier_chain_register’, declared with attribute warn_unused_result [-Werror=unused-result]
blocking_notifier_chain_register(&x86_mce_decoder_chain, nb);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Drop the WARN too, while at it.
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Ayush Sawal <ayush.sawal@...lsio.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Rohit Maheshwari <rohitm@...lsio.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Vinay Kumar Yadav <vinay.yadav@...lsio.com>
Cc: alsa-devel@...a-project.org
Cc: bcm-kernel-feedback-list@...adcom.com
Cc: intel-gfx@...ts.freedesktop.org
Cc: intel-gvt-dev@...ts.freedesktop.org
Cc: linux-alpha@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-clk@...r.kernel.org
Cc: linux-crypto@...r.kernel.org
Cc: linux-edac@...r.kernel.org
Cc: linux-fbdev@...r.kernel.org
Cc: linux-hyperv@...r.kernel.org
Cc: linux-iio@...r.kernel.org
Cc: linux-leds@...r.kernel.org
Cc: linux-mips@...r.kernel.org
Cc: linux-parisc@...r.kernel.org
Cc: linux-pm@...r.kernel.org
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: linux-remoteproc@...r.kernel.org
Cc: linux-renesas-soc@...r.kernel.org
Cc: linux-s390@...r.kernel.org
Cc: linux-scsi@...r.kernel.org
Cc: linux-sh@...r.kernel.org
Cc: linux-staging@...ts.linux.dev
Cc: linux-tegra@...r.kernel.org
Cc: linux-um@...ts.infradead.org
Cc: linux-usb@...r.kernel.org
Cc: linux-xtensa@...ux-xtensa.org
Cc: netdev@...r.kernel.org
Cc: openipmi-developer@...ts.sourceforge.net
Cc: rcu@...r.kernel.org
Cc: sparclinux@...r.kernel.org
Cc: x86@...nel.org
Cc: xen-devel@...ts.xenproject.org
---
include/linux/notifier.h | 8 ++++----
kernel/notifier.c | 36 +++++++++++++++++++-----------------
2 files changed, 23 insertions(+), 21 deletions(-)
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 87069b8459af..45cc5a8d0fd8 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -141,13 +141,13 @@ extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
#ifdef __KERNEL__
-extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
+extern int __must_check atomic_notifier_chain_register(struct atomic_notifier_head *nh,
struct notifier_block *nb);
-extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
+extern int __must_check blocking_notifier_chain_register(struct blocking_notifier_head *nh,
struct notifier_block *nb);
-extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
+extern int __must_check raw_notifier_chain_register(struct raw_notifier_head *nh,
struct notifier_block *nb);
-extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
+extern int __must_check srcu_notifier_chain_register(struct srcu_notifier_head *nh,
struct notifier_block *nb);
extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
diff --git a/kernel/notifier.c b/kernel/notifier.c
index b8251dc0bc0f..451ef3f73ad2 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -20,13 +20,11 @@ BLOCKING_NOTIFIER_HEAD(reboot_notifier_list);
*/
static int notifier_chain_register(struct notifier_block **nl,
- struct notifier_block *n)
+ struct notifier_block *n)
{
while ((*nl) != NULL) {
- if (unlikely((*nl) == n)) {
- WARN(1, "double register detected");
- return 0;
- }
+ if (unlikely((*nl) == n))
+ return -EEXIST;
if (n->priority > (*nl)->priority)
break;
nl = &((*nl)->next);
@@ -134,10 +132,11 @@ 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, %-EEXIST on error.
*/
-int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
- struct notifier_block *n)
+int __must_check
+atomic_notifier_chain_register(struct atomic_notifier_head *nh,
+ struct notifier_block *n)
{
unsigned long flags;
int ret;
@@ -216,10 +215,11 @@ 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, %-EEXIST on error.
*/
-int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
- struct notifier_block *n)
+int __must_check
+blocking_notifier_chain_register(struct blocking_notifier_head *nh,
+ struct notifier_block *n)
{
int ret;
@@ -335,10 +335,11 @@ 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, %-EEXIST on error.
*/
-int raw_notifier_chain_register(struct raw_notifier_head *nh,
- struct notifier_block *n)
+int __must_check
+raw_notifier_chain_register(struct raw_notifier_head *nh,
+ struct notifier_block *n)
{
return notifier_chain_register(&nh->head, n);
}
@@ -406,10 +407,11 @@ 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, %-EEXIST on error.
*/
-int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
- struct notifier_block *n)
+int __must_check
+srcu_notifier_chain_register(struct srcu_notifier_head *nh,
+ struct notifier_block *n)
{
int ret;
--
2.29.2
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