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 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@linutronix.de Signed-off-by: Borislav Petkov bp@suse.de Cc: Arnd Bergmann arnd@arndb.de Cc: Ayush Sawal ayush.sawal@chelsio.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Rohit Maheshwari rohitm@chelsio.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Vinay Kumar Yadav vinay.yadav@chelsio.com Cc: alsa-devel@alsa-project.org Cc: bcm-kernel-feedback-list@broadcom.com Cc: intel-gfx@lists.freedesktop.org Cc: intel-gvt-dev@lists.freedesktop.org Cc: linux-alpha@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-clk@vger.kernel.org Cc: linux-crypto@vger.kernel.org Cc: linux-edac@vger.kernel.org Cc: linux-fbdev@vger.kernel.org Cc: linux-hyperv@vger.kernel.org Cc: linux-iio@vger.kernel.org Cc: linux-leds@vger.kernel.org Cc: linux-mips@vger.kernel.org Cc: linux-parisc@vger.kernel.org Cc: linux-pm@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Cc: linux-remoteproc@vger.kernel.org Cc: linux-renesas-soc@vger.kernel.org Cc: linux-s390@vger.kernel.org Cc: linux-scsi@vger.kernel.org Cc: linux-sh@vger.kernel.org Cc: linux-staging@lists.linux.dev Cc: linux-tegra@vger.kernel.org Cc: linux-um@lists.infradead.org Cc: linux-usb@vger.kernel.org Cc: linux-xtensa@linux-xtensa.org Cc: netdev@vger.kernel.org Cc: openipmi-developer@lists.sourceforge.net Cc: rcu@vger.kernel.org Cc: sparclinux@vger.kernel.org Cc: x86@kernel.org Cc: xen-devel@lists.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;