From: Borislav Petkov <b...@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.jo...@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 <t...@linutronix.de> Signed-off-by: Borislav Petkov <b...@suse.de> Cc: Arnd Bergmann <a...@arndb.de> Cc: Ayush Sawal <ayush.sa...@chelsio.com> Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org> Cc: Rohit Maheshwari <roh...@chelsio.com> Cc: Steven Rostedt <rost...@goodmis.org> Cc: Vinay Kumar Yadav <vinay.ya...@chelsio.com> Cc: alsa-de...@alsa-project.org Cc: bcm-kernel-feedback-l...@broadcom.com Cc: intel-...@lists.freedesktop.org Cc: intel-gvt-...@lists.freedesktop.org Cc: linux-al...@vger.kernel.org Cc: linux-arm-ker...@lists.infradead.org Cc: linux-arm-ker...@lists.infradead.org Cc: linux-...@vger.kernel.org Cc: linux-cry...@vger.kernel.org Cc: linux-e...@vger.kernel.org Cc: linux-fb...@vger.kernel.org Cc: linux-hyp...@vger.kernel.org Cc: linux-...@vger.kernel.org Cc: linux-l...@vger.kernel.org Cc: linux-m...@vger.kernel.org Cc: linux-par...@vger.kernel.org Cc: linux...@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Cc: linux-remotep...@vger.kernel.org Cc: linux-renesas-...@vger.kernel.org Cc: linux-s...@vger.kernel.org Cc: linux-s...@vger.kernel.org Cc: linux...@vger.kernel.org Cc: linux-stag...@lists.linux.dev Cc: linux-te...@vger.kernel.org Cc: linux...@lists.infradead.org Cc: linux-...@vger.kernel.org Cc: linux-xte...@linux-xtensa.org Cc: net...@vger.kernel.org Cc: openipmi-develo...@lists.sourceforge.net Cc: r...@vger.kernel.org Cc: sparcli...@vger.kernel.org Cc: x...@kernel.org Cc: xen-de...@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; -- 2.29.2
