From: Michal Hocko <mhocko@kernel.org> To: Dan Streetman <ddstreet@ieee.org> Cc: Yu Zhao <yuzhao@google.com>, Seth Jennings <sjenning@redhat.com>, Linux-MM <linux-mm@kvack.org>, linux-kernel <linux-kernel@vger.kernel.org> Subject: Re: [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y Date: Fri, 2 Dec 2016 15:44:40 +0100 [thread overview] Message-ID: <20161202144440.GQ6830@dhcp22.suse.cz> (raw) In-Reply-To: <20161202143848.GP6830@dhcp22.suse.cz> On Fri 02-12-16 15:38:48, Michal Hocko wrote: > On Fri 02-12-16 09:24:35, Dan Streetman wrote: > > On Fri, Dec 2, 2016 at 8:46 AM, Michal Hocko <mhocko@kernel.org> wrote: > > > On Wed 30-11-16 13:15:16, Yu Zhao wrote: > > >> __unregister_cpu_notifier() only removes registered notifier from its > > >> linked list when CPU hotplug is configured. If we free registered CPU > > >> notifier when HOTPLUG_CPU=n, we corrupt the linked list. > > >> > > >> To fix the problem, we can either use a static CPU notifier that walks > > >> through each pool or just simply disable CPU notifier when CPU hotplug > > >> is not configured (which is perfectly safe because the code in question > > >> is called after all possible CPUs are online and will remain online > > >> until power off). > > >> > > >> v2: #ifdef for cpu_notifier_register_done during cleanup. > > > > > > this ifedfery is just ugly as hell. I am also wondering whether it is > > > really needed. __register_cpu_notifier and __unregister_cpu_notifier are > > > noops for CONFIG_HOTPLUG_CPU=n. So what's exactly that is broken here? > > > > hmm, that's interesting, __unregister_cpu_notifier is always a noop if > > HOTPLUG_CPU=n, but __register_cpu_notifier is only a noop if > > HOTPLUG_CPU=n *and* MODULE. If !MODULE, __register_cpu_notifier does > > OK, I've missed the MODULE part > > > actually register! This was added by commit > > 47e627bc8c9a70392d2049e6af5bd55fae61fe53 ('hotplug: Allow modules to > > use the cpu hotplug notifiers even if !CONFIG_HOTPLUG_CPU') and looks > > like it's to allow built-ins to register so they can notice during > > boot when cpus are initialized. > > I cannot say I wound understand the motivation but that is not really > all that important. > > > IMHO, that is the real problem - sure, without HOTPLUG_CPU, nobody > > should ever get a notification that a cpu is dying, but that doesn't > > mean builtins that register notifiers will never unregister their > > notifiers and then free them. > > Yes that is true. That suggests that __unregister_cpu_notifier should > the the symmetric thing to the __register_cpu_notifier for > CONFIG_MODULE, right? I meant the following. Completely untested --- diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 797d9c8e9a1b..8d7b473426af 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -120,6 +120,7 @@ extern void __unregister_cpu_notifier(struct notifier_block *nb); #ifndef MODULE extern int register_cpu_notifier(struct notifier_block *nb); extern int __register_cpu_notifier(struct notifier_block *nb); +extern void __unregister_cpu_notifier(struct notifier_block *nb); #else static inline int register_cpu_notifier(struct notifier_block *nb) { -- Michal Hocko SUSE Labs
WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@kernel.org> To: Dan Streetman <ddstreet@ieee.org> Cc: Yu Zhao <yuzhao@google.com>, Seth Jennings <sjenning@redhat.com>, Linux-MM <linux-mm@kvack.org>, linux-kernel <linux-kernel@vger.kernel.org> Subject: Re: [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y Date: Fri, 2 Dec 2016 15:44:40 +0100 [thread overview] Message-ID: <20161202144440.GQ6830@dhcp22.suse.cz> (raw) In-Reply-To: <20161202143848.GP6830@dhcp22.suse.cz> On Fri 02-12-16 15:38:48, Michal Hocko wrote: > On Fri 02-12-16 09:24:35, Dan Streetman wrote: > > On Fri, Dec 2, 2016 at 8:46 AM, Michal Hocko <mhocko@kernel.org> wrote: > > > On Wed 30-11-16 13:15:16, Yu Zhao wrote: > > >> __unregister_cpu_notifier() only removes registered notifier from its > > >> linked list when CPU hotplug is configured. If we free registered CPU > > >> notifier when HOTPLUG_CPU=n, we corrupt the linked list. > > >> > > >> To fix the problem, we can either use a static CPU notifier that walks > > >> through each pool or just simply disable CPU notifier when CPU hotplug > > >> is not configured (which is perfectly safe because the code in question > > >> is called after all possible CPUs are online and will remain online > > >> until power off). > > >> > > >> v2: #ifdef for cpu_notifier_register_done during cleanup. > > > > > > this ifedfery is just ugly as hell. I am also wondering whether it is > > > really needed. __register_cpu_notifier and __unregister_cpu_notifier are > > > noops for CONFIG_HOTPLUG_CPU=n. So what's exactly that is broken here? > > > > hmm, that's interesting, __unregister_cpu_notifier is always a noop if > > HOTPLUG_CPU=n, but __register_cpu_notifier is only a noop if > > HOTPLUG_CPU=n *and* MODULE. If !MODULE, __register_cpu_notifier does > > OK, I've missed the MODULE part > > > actually register! This was added by commit > > 47e627bc8c9a70392d2049e6af5bd55fae61fe53 ('hotplug: Allow modules to > > use the cpu hotplug notifiers even if !CONFIG_HOTPLUG_CPU') and looks > > like it's to allow built-ins to register so they can notice during > > boot when cpus are initialized. > > I cannot say I wound understand the motivation but that is not really > all that important. > > > IMHO, that is the real problem - sure, without HOTPLUG_CPU, nobody > > should ever get a notification that a cpu is dying, but that doesn't > > mean builtins that register notifiers will never unregister their > > notifiers and then free them. > > Yes that is true. That suggests that __unregister_cpu_notifier should > the the symmetric thing to the __register_cpu_notifier for > CONFIG_MODULE, right? I meant the following. Completely untested --- diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 797d9c8e9a1b..8d7b473426af 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -120,6 +120,7 @@ extern void __unregister_cpu_notifier(struct notifier_block *nb); #ifndef MODULE extern int register_cpu_notifier(struct notifier_block *nb); extern int __register_cpu_notifier(struct notifier_block *nb); +extern void __unregister_cpu_notifier(struct notifier_block *nb); #else static inline int register_cpu_notifier(struct notifier_block *nb) { -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-12-02 14:44 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-11-30 21:15 [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y Yu Zhao 2016-11-30 21:15 ` Yu Zhao 2016-12-02 13:46 ` Michal Hocko 2016-12-02 13:46 ` Michal Hocko 2016-12-02 14:24 ` Dan Streetman 2016-12-02 14:24 ` Dan Streetman 2016-12-02 14:38 ` Michal Hocko 2016-12-02 14:38 ` Michal Hocko 2016-12-02 14:44 ` Michal Hocko [this message] 2016-12-02 14:44 ` Michal Hocko 2016-12-02 14:56 ` Dan Streetman 2016-12-02 14:56 ` Dan Streetman 2016-12-02 15:19 ` [PATCH] hotplug: make register and unregister notifier API symmetric Michal Hocko 2016-12-02 15:19 ` Michal Hocko 2016-12-03 5:15 ` kbuild test robot 2016-12-05 6:08 ` Michal Hocko 2016-12-05 6:08 ` Michal Hocko 2016-12-03 7:18 ` kbuild test robot 2016-12-05 20:59 ` Yu Zhao 2016-12-05 20:59 ` Yu Zhao 2016-12-06 9:30 ` Michal Hocko 2016-12-06 9:30 ` Michal Hocko 2016-12-05 21:11 ` [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y Yu Zhao 2016-12-05 21:11 ` Yu Zhao
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