* [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y @ 2016-11-30 21:15 Yu Zhao 2016-12-02 13:46 ` Michal Hocko 0 siblings, 1 reply; 13+ messages in thread From: Yu Zhao @ 2016-11-30 21:15 UTC (permalink / raw) To: Seth Jennings, Dan Streetman; +Cc: linux-mm, linux-kernel, Yu Zhao __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. Signe-off-by: Yu Zhao <yuzhao@google.com> --- mm/zswap.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/mm/zswap.c b/mm/zswap.c index 275b22c..2915f44 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -118,7 +118,9 @@ struct zswap_pool { struct kref kref; struct list_head list; struct work_struct work; +#ifdef CONFIG_HOTPLUG_CPU struct notifier_block notifier; +#endif char tfm_name[CRYPTO_MAX_ALG_NAME]; }; @@ -448,6 +450,7 @@ static int __zswap_cpu_comp_notifier(struct zswap_pool *pool, return NOTIFY_OK; } +#ifdef CONFIG_HOTPLUG_CPU static int zswap_cpu_comp_notifier(struct notifier_block *nb, unsigned long action, void *pcpu) { @@ -456,27 +459,34 @@ static int zswap_cpu_comp_notifier(struct notifier_block *nb, return __zswap_cpu_comp_notifier(pool, action, cpu); } +#endif static int zswap_cpu_comp_init(struct zswap_pool *pool) { unsigned long cpu; +#ifdef CONFIG_HOTPLUG_CPU memset(&pool->notifier, 0, sizeof(pool->notifier)); pool->notifier.notifier_call = zswap_cpu_comp_notifier; cpu_notifier_register_begin(); +#endif for_each_online_cpu(cpu) if (__zswap_cpu_comp_notifier(pool, CPU_UP_PREPARE, cpu) == NOTIFY_BAD) goto cleanup; +#ifdef CONFIG_HOTPLUG_CPU __register_cpu_notifier(&pool->notifier); cpu_notifier_register_done(); +#endif return 0; cleanup: for_each_online_cpu(cpu) __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu); +#ifdef CONFIG_HOTPLUG_CPU cpu_notifier_register_done(); +#endif return -ENOMEM; } @@ -484,11 +494,15 @@ static void zswap_cpu_comp_destroy(struct zswap_pool *pool) { unsigned long cpu; +#ifdef CONFIG_HOTPLUG_CPU cpu_notifier_register_begin(); +#endif for_each_online_cpu(cpu) __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu); +#ifdef CONFIG_HOTPLUG_CPU __unregister_cpu_notifier(&pool->notifier); cpu_notifier_register_done(); +#endif } /********************************* -- 2.8.0.rc3.226.g39d4020 -- 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> ^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y 2016-11-30 21:15 [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y Yu Zhao @ 2016-12-02 13:46 ` Michal Hocko 2016-12-02 14:24 ` Dan Streetman 2016-12-05 21:11 ` [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y Yu Zhao 0 siblings, 2 replies; 13+ messages in thread From: Michal Hocko @ 2016-12-02 13:46 UTC (permalink / raw) To: Yu Zhao; +Cc: Seth Jennings, Dan Streetman, linux-mm, linux-kernel 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? > Signe-off-by: Yu Zhao <yuzhao@google.com> > --- > mm/zswap.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/mm/zswap.c b/mm/zswap.c > index 275b22c..2915f44 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -118,7 +118,9 @@ struct zswap_pool { > struct kref kref; > struct list_head list; > struct work_struct work; > +#ifdef CONFIG_HOTPLUG_CPU > struct notifier_block notifier; > +#endif > char tfm_name[CRYPTO_MAX_ALG_NAME]; > }; > > @@ -448,6 +450,7 @@ static int __zswap_cpu_comp_notifier(struct zswap_pool *pool, > return NOTIFY_OK; > } > > +#ifdef CONFIG_HOTPLUG_CPU > static int zswap_cpu_comp_notifier(struct notifier_block *nb, > unsigned long action, void *pcpu) > { > @@ -456,27 +459,34 @@ static int zswap_cpu_comp_notifier(struct notifier_block *nb, > > return __zswap_cpu_comp_notifier(pool, action, cpu); > } > +#endif > > static int zswap_cpu_comp_init(struct zswap_pool *pool) > { > unsigned long cpu; > > +#ifdef CONFIG_HOTPLUG_CPU > memset(&pool->notifier, 0, sizeof(pool->notifier)); > pool->notifier.notifier_call = zswap_cpu_comp_notifier; > > cpu_notifier_register_begin(); > +#endif > for_each_online_cpu(cpu) > if (__zswap_cpu_comp_notifier(pool, CPU_UP_PREPARE, cpu) == > NOTIFY_BAD) > goto cleanup; > +#ifdef CONFIG_HOTPLUG_CPU > __register_cpu_notifier(&pool->notifier); > cpu_notifier_register_done(); > +#endif > return 0; > > cleanup: > for_each_online_cpu(cpu) > __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu); > +#ifdef CONFIG_HOTPLUG_CPU > cpu_notifier_register_done(); > +#endif > return -ENOMEM; > } > > @@ -484,11 +494,15 @@ static void zswap_cpu_comp_destroy(struct zswap_pool *pool) > { > unsigned long cpu; > > +#ifdef CONFIG_HOTPLUG_CPU > cpu_notifier_register_begin(); > +#endif > for_each_online_cpu(cpu) > __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu); > +#ifdef CONFIG_HOTPLUG_CPU > __unregister_cpu_notifier(&pool->notifier); > cpu_notifier_register_done(); > +#endif > } > > /********************************* > -- > 2.8.0.rc3.226.g39d4020 > > -- > 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> -- 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> ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y 2016-12-02 13:46 ` Michal Hocko @ 2016-12-02 14:24 ` Dan Streetman 2016-12-02 14:38 ` Michal Hocko 2016-12-05 21:11 ` [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y Yu Zhao 1 sibling, 1 reply; 13+ messages in thread From: Dan Streetman @ 2016-12-02 14:24 UTC (permalink / raw) To: Michal Hocko; +Cc: Yu Zhao, Seth Jennings, Linux-MM, linux-kernel 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 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. 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. Changing zswap is only working around the symptom; instead, hotplug should be changed to provide unregister_cpu_notifier in all cases where register_cpu_notifier is provided. > >> Signe-off-by: Yu Zhao <yuzhao@google.com> >> --- >> mm/zswap.c | 14 ++++++++++++++ >> 1 file changed, 14 insertions(+) >> >> diff --git a/mm/zswap.c b/mm/zswap.c >> index 275b22c..2915f44 100644 >> --- a/mm/zswap.c >> +++ b/mm/zswap.c >> @@ -118,7 +118,9 @@ struct zswap_pool { >> struct kref kref; >> struct list_head list; >> struct work_struct work; >> +#ifdef CONFIG_HOTPLUG_CPU >> struct notifier_block notifier; >> +#endif >> char tfm_name[CRYPTO_MAX_ALG_NAME]; >> }; >> >> @@ -448,6 +450,7 @@ static int __zswap_cpu_comp_notifier(struct zswap_pool *pool, >> return NOTIFY_OK; >> } >> >> +#ifdef CONFIG_HOTPLUG_CPU >> static int zswap_cpu_comp_notifier(struct notifier_block *nb, >> unsigned long action, void *pcpu) >> { >> @@ -456,27 +459,34 @@ static int zswap_cpu_comp_notifier(struct notifier_block *nb, >> >> return __zswap_cpu_comp_notifier(pool, action, cpu); >> } >> +#endif >> >> static int zswap_cpu_comp_init(struct zswap_pool *pool) >> { >> unsigned long cpu; >> >> +#ifdef CONFIG_HOTPLUG_CPU >> memset(&pool->notifier, 0, sizeof(pool->notifier)); >> pool->notifier.notifier_call = zswap_cpu_comp_notifier; >> >> cpu_notifier_register_begin(); >> +#endif >> for_each_online_cpu(cpu) >> if (__zswap_cpu_comp_notifier(pool, CPU_UP_PREPARE, cpu) == >> NOTIFY_BAD) >> goto cleanup; >> +#ifdef CONFIG_HOTPLUG_CPU >> __register_cpu_notifier(&pool->notifier); >> cpu_notifier_register_done(); >> +#endif >> return 0; >> >> cleanup: >> for_each_online_cpu(cpu) >> __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu); >> +#ifdef CONFIG_HOTPLUG_CPU >> cpu_notifier_register_done(); >> +#endif >> return -ENOMEM; >> } >> >> @@ -484,11 +494,15 @@ static void zswap_cpu_comp_destroy(struct zswap_pool *pool) >> { >> unsigned long cpu; >> >> +#ifdef CONFIG_HOTPLUG_CPU >> cpu_notifier_register_begin(); >> +#endif >> for_each_online_cpu(cpu) >> __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu); >> +#ifdef CONFIG_HOTPLUG_CPU >> __unregister_cpu_notifier(&pool->notifier); >> cpu_notifier_register_done(); >> +#endif >> } >> >> /********************************* >> -- >> 2.8.0.rc3.226.g39d4020 >> >> -- >> 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> > > -- > 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> ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y 2016-12-02 14:24 ` Dan Streetman @ 2016-12-02 14:38 ` Michal Hocko 2016-12-02 14:44 ` Michal Hocko 0 siblings, 1 reply; 13+ messages in thread From: Michal Hocko @ 2016-12-02 14:38 UTC (permalink / raw) To: Dan Streetman; +Cc: Yu Zhao, Seth Jennings, Linux-MM, linux-kernel 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? > Changing zswap is only working around the symptom; instead, hotplug > should be changed to provide unregister_cpu_notifier in all cases > where register_cpu_notifier is provided. Agreed. > >> Signe-off-by: Yu Zhao <yuzhao@google.com> > >> --- > >> mm/zswap.c | 14 ++++++++++++++ > >> 1 file changed, 14 insertions(+) > >> > >> diff --git a/mm/zswap.c b/mm/zswap.c > >> index 275b22c..2915f44 100644 > >> --- a/mm/zswap.c > >> +++ b/mm/zswap.c > >> @@ -118,7 +118,9 @@ struct zswap_pool { > >> struct kref kref; > >> struct list_head list; > >> struct work_struct work; > >> +#ifdef CONFIG_HOTPLUG_CPU > >> struct notifier_block notifier; > >> +#endif > >> char tfm_name[CRYPTO_MAX_ALG_NAME]; > >> }; > >> > >> @@ -448,6 +450,7 @@ static int __zswap_cpu_comp_notifier(struct zswap_pool *pool, > >> return NOTIFY_OK; > >> } > >> > >> +#ifdef CONFIG_HOTPLUG_CPU > >> static int zswap_cpu_comp_notifier(struct notifier_block *nb, > >> unsigned long action, void *pcpu) > >> { > >> @@ -456,27 +459,34 @@ static int zswap_cpu_comp_notifier(struct notifier_block *nb, > >> > >> return __zswap_cpu_comp_notifier(pool, action, cpu); > >> } > >> +#endif > >> > >> static int zswap_cpu_comp_init(struct zswap_pool *pool) > >> { > >> unsigned long cpu; > >> > >> +#ifdef CONFIG_HOTPLUG_CPU > >> memset(&pool->notifier, 0, sizeof(pool->notifier)); > >> pool->notifier.notifier_call = zswap_cpu_comp_notifier; > >> > >> cpu_notifier_register_begin(); > >> +#endif > >> for_each_online_cpu(cpu) > >> if (__zswap_cpu_comp_notifier(pool, CPU_UP_PREPARE, cpu) == > >> NOTIFY_BAD) > >> goto cleanup; > >> +#ifdef CONFIG_HOTPLUG_CPU > >> __register_cpu_notifier(&pool->notifier); > >> cpu_notifier_register_done(); > >> +#endif > >> return 0; > >> > >> cleanup: > >> for_each_online_cpu(cpu) > >> __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu); > >> +#ifdef CONFIG_HOTPLUG_CPU > >> cpu_notifier_register_done(); > >> +#endif > >> return -ENOMEM; > >> } > >> > >> @@ -484,11 +494,15 @@ static void zswap_cpu_comp_destroy(struct zswap_pool *pool) > >> { > >> unsigned long cpu; > >> > >> +#ifdef CONFIG_HOTPLUG_CPU > >> cpu_notifier_register_begin(); > >> +#endif > >> for_each_online_cpu(cpu) > >> __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu); > >> +#ifdef CONFIG_HOTPLUG_CPU > >> __unregister_cpu_notifier(&pool->notifier); > >> cpu_notifier_register_done(); > >> +#endif > >> } > >> > >> /********************************* > >> -- > >> 2.8.0.rc3.226.g39d4020 > >> > >> -- > >> 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> > > > > -- > > Michal Hocko > > SUSE Labs -- 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> ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y 2016-12-02 14:38 ` Michal Hocko @ 2016-12-02 14:44 ` Michal Hocko 2016-12-02 14:56 ` Dan Streetman 0 siblings, 1 reply; 13+ messages in thread From: Michal Hocko @ 2016-12-02 14:44 UTC (permalink / raw) To: Dan Streetman; +Cc: Yu Zhao, Seth Jennings, Linux-MM, linux-kernel 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> ^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y 2016-12-02 14:44 ` Michal Hocko @ 2016-12-02 14:56 ` Dan Streetman 2016-12-02 15:19 ` [PATCH] hotplug: make register and unregister notifier API symmetric Michal Hocko 0 siblings, 1 reply; 13+ messages in thread From: Dan Streetman @ 2016-12-02 14:56 UTC (permalink / raw) To: Michal Hocko; +Cc: Yu Zhao, Seth Jennings, Linux-MM, linux-kernel On Fri, Dec 2, 2016 at 9:44 AM, Michal Hocko <mhocko@kernel.org> wrote: > 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 agreed, but also needs the non-__ version, and kernel/cpu.c needs tweaking to move those functions out of the #ifdef CONFIG_HOTPLUG_CPU section. > --- > 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> ^ permalink raw reply [flat|nested] 13+ messages in thread
* [PATCH] hotplug: make register and unregister notifier API symmetric 2016-12-02 14:56 ` Dan Streetman @ 2016-12-02 15:19 ` Michal Hocko 2016-12-03 5:15 ` kbuild test robot ` (2 more replies) 0 siblings, 3 replies; 13+ messages in thread From: Michal Hocko @ 2016-12-02 15:19 UTC (permalink / raw) To: Dan Streetman Cc: Yu Zhao, Seth Jennings, Linux-MM, linux-kernel, Avi Kivity, Thomas Gleixner, Ingo Molnar [Let's CC more people - the thread started http://lkml.kernel.org/r/1480540516-6458-1-git-send-email-yuzhao@google.com] On Fri 02-12-16 09:56:26, Dan Streetman wrote: > On Fri, Dec 2, 2016 at 9:44 AM, Michal Hocko <mhocko@kernel.org> wrote: > > 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 > > agreed, but also needs the non-__ version, and kernel/cpu.c needs > tweaking to move those functions out of the #ifdef CONFIG_HOTPLUG_CPU > section. OK, this is still only compile tested. Yu Zhao, assuming you were able to trigger the original problem could you test with the below patch please? --- ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] hotplug: make register and unregister notifier API symmetric 2016-12-02 15:19 ` [PATCH] hotplug: make register and unregister notifier API symmetric Michal Hocko @ 2016-12-03 5:15 ` kbuild test robot 2016-12-05 6:08 ` Michal Hocko 2016-12-03 7:18 ` kbuild test robot 2016-12-05 20:59 ` Yu Zhao 2 siblings, 1 reply; 13+ messages in thread From: kbuild test robot @ 2016-12-03 5:15 UTC (permalink / raw) To: Michal Hocko Cc: kbuild-all, Dan Streetman, Yu Zhao, Seth Jennings, Linux-MM, linux-kernel, Avi Kivity, Thomas Gleixner, Ingo Molnar [-- Attachment #1: Type: text/plain, Size: 1030 bytes --] Hi Michal, [auto build test ERROR on linus/master] [also build test ERROR on v4.9-rc7 next-20161202] [if your patch is applied to the wrong git tree, please drop us a note to help improve the system] url: https://github.com/0day-ci/linux/commits/Michal-Hocko/hotplug-make-register-and-unregister-notifier-API-symmetric/20161203-114815 config: i386-randconfig-r0-201648 (attached as .config) compiler: gcc-5 (Debian 5.4.1-2) 5.4.1 20160904 reproduce: # save the attached .config to linux build tree make ARCH=i386 All errors (new ones prefixed by >>): arch/x86/oprofile/built-in.o: In function `nmi_timer_shutdown': >> nmi_timer_int.c:(.text+0x238b): undefined reference to `__unregister_cpu_notifier' arch/x86/oprofile/built-in.o: In function `nmi_shutdown': nmi_int.c:(.text+0x2793): undefined reference to `__unregister_cpu_notifier' --- 0-DAY kernel test infrastructure Open Source Technology Center https://lists.01.org/pipermail/kbuild-all Intel Corporation [-- Attachment #2: .config.gz --] [-- Type: application/gzip, Size: 21659 bytes --] ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] hotplug: make register and unregister notifier API symmetric 2016-12-03 5:15 ` kbuild test robot @ 2016-12-05 6:08 ` Michal Hocko 0 siblings, 0 replies; 13+ messages in thread From: Michal Hocko @ 2016-12-05 6:08 UTC (permalink / raw) To: kbuild test robot Cc: kbuild-all, Dan Streetman, Yu Zhao, Seth Jennings, Linux-MM, linux-kernel, Avi Kivity, Thomas Gleixner, Ingo Molnar On Sat 03-12-16 13:15:42, kbuild test robot wrote: > Hi Michal, > > [auto build test ERROR on linus/master] > [also build test ERROR on v4.9-rc7 next-20161202] > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system] > > url: https://github.com/0day-ci/linux/commits/Michal-Hocko/hotplug-make-register-and-unregister-notifier-API-symmetric/20161203-114815 > config: i386-randconfig-r0-201648 (attached as .config) > compiler: gcc-5 (Debian 5.4.1-2) 5.4.1 20160904 > reproduce: > # save the attached .config to linux build tree > make ARCH=i386 > > All errors (new ones prefixed by >>): > > arch/x86/oprofile/built-in.o: In function `nmi_timer_shutdown': > >> nmi_timer_int.c:(.text+0x238b): undefined reference to `__unregister_cpu_notifier' > arch/x86/oprofile/built-in.o: In function `nmi_shutdown': > nmi_int.c:(.text+0x2793): undefined reference to `__unregister_cpu_notifier' Ohh, right. I have missed that unregister functions definitions are guarded as well. This patch should hopefully be correct finally. Please note it also exports register/unregister callbacks when CONFIG_HOTPLUG_CPU is not defined which is not really needed strictly speaking because those are only used when !MODULE but I would rather not make the code more complicated. If maintainers prefer I can guard exports separately of course. --- ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] hotplug: make register and unregister notifier API symmetric 2016-12-02 15:19 ` [PATCH] hotplug: make register and unregister notifier API symmetric Michal Hocko 2016-12-03 5:15 ` kbuild test robot @ 2016-12-03 7:18 ` kbuild test robot 2016-12-05 20:59 ` Yu Zhao 2 siblings, 0 replies; 13+ messages in thread From: kbuild test robot @ 2016-12-03 7:18 UTC (permalink / raw) To: Michal Hocko Cc: kbuild-all, Dan Streetman, Yu Zhao, Seth Jennings, Linux-MM, linux-kernel, Avi Kivity, Thomas Gleixner, Ingo Molnar [-- Attachment #1: Type: text/plain, Size: 1179 bytes --] Hi Michal, [auto build test ERROR on linus/master] [also build test ERROR on v4.9-rc7 next-20161202] [if your patch is applied to the wrong git tree, please drop us a note to help improve the system] url: https://github.com/0day-ci/linux/commits/Michal-Hocko/hotplug-make-register-and-unregister-notifier-API-symmetric/20161203-114815 config: i386-randconfig-s1-201648 (attached as .config) compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901 reproduce: # save the attached .config to linux build tree make ARCH=i386 All errors (new ones prefixed by >>): mm/built-in.o: In function `zs_unregister_cpu_notifier': >> zsmalloc.c:(.text.unlikely+0xc7e): undefined reference to `__unregister_cpu_notifier' arch/x86/oprofile/built-in.o: In function `nmi_timer_shutdown': nmi_timer_int.c:(.text+0x1c7d): undefined reference to `__unregister_cpu_notifier' arch/x86/oprofile/built-in.o: In function `nmi_shutdown': nmi_int.c:(.text+0x2319): undefined reference to `__unregister_cpu_notifier' --- 0-DAY kernel test infrastructure Open Source Technology Center https://lists.01.org/pipermail/kbuild-all Intel Corporation [-- Attachment #2: .config.gz --] [-- Type: application/gzip, Size: 21074 bytes --] ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] hotplug: make register and unregister notifier API symmetric 2016-12-02 15:19 ` [PATCH] hotplug: make register and unregister notifier API symmetric Michal Hocko 2016-12-03 5:15 ` kbuild test robot 2016-12-03 7:18 ` kbuild test robot @ 2016-12-05 20:59 ` Yu Zhao 2016-12-06 9:30 ` Michal Hocko 2 siblings, 1 reply; 13+ messages in thread From: Yu Zhao @ 2016-12-05 20:59 UTC (permalink / raw) To: Michal Hocko Cc: Dan Streetman, Seth Jennings, Linux-MM, linux-kernel, Avi Kivity, Thomas Gleixner, Ingo Molnar On Fri, Dec 02, 2016 at 04:19:36PM +0100, Michal Hocko wrote: > [Let's CC more people - the thread started > http://lkml.kernel.org/r/1480540516-6458-1-git-send-email-yuzhao@google.com] > > On Fri 02-12-16 09:56:26, Dan Streetman wrote: > > On Fri, Dec 2, 2016 at 9:44 AM, Michal Hocko <mhocko@kernel.org> wrote: > > > 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 > > > > agreed, but also needs the non-__ version, and kernel/cpu.c needs > > tweaking to move those functions out of the #ifdef CONFIG_HOTPLUG_CPU > > section. > > OK, this is still only compile tested. Yu Zhao, assuming you were able > to trigger the original problem could you test with the below patch > please? This patch (plus the latest fix in this thread) solves the problem. Just for the record, the problem is when CONFIG_HOTPLUG_CPU=n, changing /sys/module/zswap/parameters/compressor multiple times will cause: [ 144.964346] BUG: unable to handle kernel paging request at ffff880658a2be78 [ 144.971337] IP: [<ffffffffa290b00b>] raw_notifier_chain_register+0x1b/0x40 <snipped> [ 145.122628] Call Trace: [ 145.125086] [<ffffffffa28e5cf8>] __register_cpu_notifier+0x18/0x20 [ 145.131350] [<ffffffffa2a5dd73>] zswap_pool_create+0x273/0x400 [ 145.137268] [<ffffffffa2a5e0fc>] __zswap_param_set+0x1fc/0x300 [ 145.143188] [<ffffffffa2944c1d>] ? trace_hardirqs_on+0xd/0x10 [ 145.149018] [<ffffffffa2908798>] ? kernel_param_lock+0x28/0x30 [ 145.154940] [<ffffffffa2a3e8cf>] ? __might_fault+0x4f/0xa0 [ 145.160511] [<ffffffffa2a5e237>] zswap_compressor_param_set+0x17/0x20 [ 145.167035] [<ffffffffa2908d3c>] param_attr_store+0x5c/0xb0 [ 145.172694] [<ffffffffa290848d>] module_attr_store+0x1d/0x30 [ 145.178443] [<ffffffffa2b2b41f>] sysfs_kf_write+0x4f/0x70 [ 145.183925] [<ffffffffa2b2a5b9>] kernfs_fop_write+0x149/0x180 [ 145.189761] [<ffffffffa2a99248>] __vfs_write+0x18/0x40 [ 145.194982] [<ffffffffa2a9a412>] vfs_write+0xb2/0x1a0 [ 145.200122] [<ffffffffa2a9a732>] SyS_write+0x52/0xa0 [ 145.205177] [<ffffffffa2ff4d97>] entry_SYSCALL_64_fastpath+0x12/0x17 > --- > From c812fe4e519914aa37f092d3a0321038fadcdde7 Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@suse.com> > Date: Fri, 2 Dec 2016 16:06:56 +0100 > Subject: [PATCH] hotplug: make register and unregister notifier API symmetric > > Yu Zhao has noticed that __unregister_cpu_notifier only unregisters its > notifiers when HOTPLUG_CPU=y while the registration might succeed even > when HOTPLUG_CPU=n if MODULE is enabled. This means that e.g. zswap > might keep a stale notifier on the list on the manual clean up during > the pool tear down and thus corrupt the list. Fix this issue by making > unregister APIs symmetric to the register so there are no surprises. > > Fixes: 47e627bc8c9a ("[PATCH] hotplug: Allow modules to use the cpu hotplug notifiers even if !CONFIG_HOTPLUG_CPU") > Cc: stable # zswap needs it 4.3+ > Reported-by: Yu Zhao <yuzhao@google.com> > Signed-off-by: Michal Hocko <mhocko@suse.com> > --- > include/linux/cpu.h | 15 ++++----------- > 1 file changed, 4 insertions(+), 11 deletions(-) > > diff --git a/include/linux/cpu.h b/include/linux/cpu.h > index 797d9c8e9a1b..c8938eb21e34 100644 > --- a/include/linux/cpu.h > +++ b/include/linux/cpu.h > @@ -105,22 +105,16 @@ extern bool cpuhp_tasks_frozen; > { .notifier_call = fn, .priority = pri }; \ > __register_cpu_notifier(&fn##_nb); \ > } > -#else /* #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ > -#define cpu_notifier(fn, pri) do { (void)(fn); } while (0) > -#define __cpu_notifier(fn, pri) do { (void)(fn); } while (0) > -#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ > > -#ifdef CONFIG_HOTPLUG_CPU > 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); > extern void __unregister_cpu_notifier(struct notifier_block *nb); > -#else > > -#ifndef MODULE > -extern int register_cpu_notifier(struct notifier_block *nb); > -extern int __register_cpu_notifier(struct notifier_block *nb); > -#else > +#else /* #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ > +#define cpu_notifier(fn, pri) do { (void)(fn); } while (0) > +#define __cpu_notifier(fn, pri) do { (void)(fn); } while (0) > + > static inline int register_cpu_notifier(struct notifier_block *nb) > { > return 0; > @@ -130,7 +124,6 @@ static inline int __register_cpu_notifier(struct notifier_block *nb) > { > return 0; > } > -#endif > > static inline void unregister_cpu_notifier(struct notifier_block *nb) > { > -- > 2.10.2 > > -- > 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> ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] hotplug: make register and unregister notifier API symmetric 2016-12-05 20:59 ` Yu Zhao @ 2016-12-06 9:30 ` Michal Hocko 0 siblings, 0 replies; 13+ messages in thread From: Michal Hocko @ 2016-12-06 9:30 UTC (permalink / raw) To: Yu Zhao Cc: Dan Streetman, Seth Jennings, Linux-MM, linux-kernel, Avi Kivity, Thomas Gleixner, Ingo Molnar On Mon 05-12-16 12:59:02, Yu Zhao wrote: > On Fri, Dec 02, 2016 at 04:19:36PM +0100, Michal Hocko wrote: > > [Let's CC more people - the thread started > > http://lkml.kernel.org/r/1480540516-6458-1-git-send-email-yuzhao@google.com] > > > > On Fri 02-12-16 09:56:26, Dan Streetman wrote: > > > On Fri, Dec 2, 2016 at 9:44 AM, Michal Hocko <mhocko@kernel.org> wrote: > > > > 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 > > > > > > agreed, but also needs the non-__ version, and kernel/cpu.c needs > > > tweaking to move those functions out of the #ifdef CONFIG_HOTPLUG_CPU > > > section. > > > > OK, this is still only compile tested. Yu Zhao, assuming you were able > > to trigger the original problem could you test with the below patch > > please? > > This patch (plus the latest fix in this thread) solves the problem. > > Just for the record, the problem is when CONFIG_HOTPLUG_CPU=n, changing > /sys/module/zswap/parameters/compressor multiple times will cause: > > [ 144.964346] BUG: unable to handle kernel paging request at ffff880658a2be78 > [ 144.971337] IP: [<ffffffffa290b00b>] raw_notifier_chain_register+0x1b/0x40 > <snipped> > [ 145.122628] Call Trace: > [ 145.125086] [<ffffffffa28e5cf8>] __register_cpu_notifier+0x18/0x20 > [ 145.131350] [<ffffffffa2a5dd73>] zswap_pool_create+0x273/0x400 > [ 145.137268] [<ffffffffa2a5e0fc>] __zswap_param_set+0x1fc/0x300 > [ 145.143188] [<ffffffffa2944c1d>] ? trace_hardirqs_on+0xd/0x10 > [ 145.149018] [<ffffffffa2908798>] ? kernel_param_lock+0x28/0x30 > [ 145.154940] [<ffffffffa2a3e8cf>] ? __might_fault+0x4f/0xa0 > [ 145.160511] [<ffffffffa2a5e237>] zswap_compressor_param_set+0x17/0x20 > [ 145.167035] [<ffffffffa2908d3c>] param_attr_store+0x5c/0xb0 > [ 145.172694] [<ffffffffa290848d>] module_attr_store+0x1d/0x30 > [ 145.178443] [<ffffffffa2b2b41f>] sysfs_kf_write+0x4f/0x70 > [ 145.183925] [<ffffffffa2b2a5b9>] kernfs_fop_write+0x149/0x180 > [ 145.189761] [<ffffffffa2a99248>] __vfs_write+0x18/0x40 > [ 145.194982] [<ffffffffa2a9a412>] vfs_write+0xb2/0x1a0 > [ 145.200122] [<ffffffffa2a9a732>] SyS_write+0x52/0xa0 > [ 145.205177] [<ffffffffa2ff4d97>] entry_SYSCALL_64_fastpath+0x12/0x17 Thanks for this additional information which I have added to the changelog. I have also added your Tested-by unless you have any objections and will repost soon. -- 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> ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y 2016-12-02 13:46 ` Michal Hocko 2016-12-02 14:24 ` Dan Streetman @ 2016-12-05 21:11 ` Yu Zhao 1 sibling, 0 replies; 13+ messages in thread From: Yu Zhao @ 2016-12-05 21:11 UTC (permalink / raw) To: Michal Hocko; +Cc: Seth Jennings, Dan Streetman, linux-mm, linux-kernel On Fri, Dec 02, 2016 at 02:46:06PM +0100, Michal Hocko 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? Well, I'm not a fan of ifdef and I don't like the unnecessary memory usage (notifier_block) and lock (cpu_notifier_register_begin/done) either. Just pointing this out, having no problem living with your hotplug fixes. > > > Signe-off-by: Yu Zhao <yuzhao@google.com> > > --- > > mm/zswap.c | 14 ++++++++++++++ > > 1 file changed, 14 insertions(+) > > > > diff --git a/mm/zswap.c b/mm/zswap.c > > index 275b22c..2915f44 100644 > > --- a/mm/zswap.c > > +++ b/mm/zswap.c > > @@ -118,7 +118,9 @@ struct zswap_pool { > > struct kref kref; > > struct list_head list; > > struct work_struct work; > > +#ifdef CONFIG_HOTPLUG_CPU > > struct notifier_block notifier; > > +#endif > > char tfm_name[CRYPTO_MAX_ALG_NAME]; > > }; > > > > @@ -448,6 +450,7 @@ static int __zswap_cpu_comp_notifier(struct zswap_pool *pool, > > return NOTIFY_OK; > > } > > > > +#ifdef CONFIG_HOTPLUG_CPU > > static int zswap_cpu_comp_notifier(struct notifier_block *nb, > > unsigned long action, void *pcpu) > > { > > @@ -456,27 +459,34 @@ static int zswap_cpu_comp_notifier(struct notifier_block *nb, > > > > return __zswap_cpu_comp_notifier(pool, action, cpu); > > } > > +#endif > > > > static int zswap_cpu_comp_init(struct zswap_pool *pool) > > { > > unsigned long cpu; > > > > +#ifdef CONFIG_HOTPLUG_CPU > > memset(&pool->notifier, 0, sizeof(pool->notifier)); > > pool->notifier.notifier_call = zswap_cpu_comp_notifier; > > > > cpu_notifier_register_begin(); > > +#endif > > for_each_online_cpu(cpu) > > if (__zswap_cpu_comp_notifier(pool, CPU_UP_PREPARE, cpu) == > > NOTIFY_BAD) > > goto cleanup; > > +#ifdef CONFIG_HOTPLUG_CPU > > __register_cpu_notifier(&pool->notifier); > > cpu_notifier_register_done(); > > +#endif > > return 0; > > > > cleanup: > > for_each_online_cpu(cpu) > > __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu); > > +#ifdef CONFIG_HOTPLUG_CPU > > cpu_notifier_register_done(); > > +#endif > > return -ENOMEM; > > } > > > > @@ -484,11 +494,15 @@ static void zswap_cpu_comp_destroy(struct zswap_pool *pool) > > { > > unsigned long cpu; > > > > +#ifdef CONFIG_HOTPLUG_CPU > > cpu_notifier_register_begin(); > > +#endif > > for_each_online_cpu(cpu) > > __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu); > > +#ifdef CONFIG_HOTPLUG_CPU > > __unregister_cpu_notifier(&pool->notifier); > > cpu_notifier_register_done(); > > +#endif > > } > > > > /********************************* > > -- > > 2.8.0.rc3.226.g39d4020 > > > > -- > > 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> > > -- > 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> ^ permalink raw reply [flat|nested] 13+ messages in thread
end of thread, other threads:[~2016-12-06 9:30 UTC | newest] Thread overview: 13+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2016-11-30 21:15 [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y Yu Zhao 2016-12-02 13:46 ` Michal Hocko 2016-12-02 14:24 ` Dan Streetman 2016-12-02 14:38 ` Michal Hocko 2016-12-02 14:44 ` Michal Hocko 2016-12-02 14:56 ` Dan Streetman 2016-12-02 15:19 ` [PATCH] hotplug: make register and unregister notifier API symmetric Michal Hocko 2016-12-03 5:15 ` kbuild test robot 2016-12-05 6:08 ` Michal Hocko 2016-12-03 7:18 ` kbuild test robot 2016-12-05 20:59 ` Yu Zhao 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
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