From: Gautham R Shenoy Since 2.6.18-something, the community has been bugged by the problem to provide a clean and a stable mechanism to postpone a cpu-hotplug event as lock_cpu_hotplug was badly broken. This is another proposal towards solving that problem. This one is along the lines of the solution provided in kernel/workqueue.c Instead of having a global mechanism like lock_cpu_hotplug, we allow the subsytems to define their own per-subsystem hot cpu mutexes. These would be taken(released) where ever we are currently calling lock_cpu_hotplug(unlock_cpu_hotplug). Also, in the per-subsystem hotcpu callback function,we take this mutex before we handle any pre-cpu-hotplug events and release it once we finish handling the post-cpu-hotplug events. A standard means for doing this has been provided in [PATCH 2/4] and demonstrated in [PATCH 3/4]. The ordering of these per-subsystem mutexes might still prove to be a problem, but hopefully lockdep should help us get out of that muddle. The patch set to be applied against linux-2.6.19-rc5 is as follows: [PATCH 1/4] : Extend notifier_call_chain with an option to specify the number of notifications to be sent and also count the number of notifications actually sent. [PATCH 2/4] : Define events CPU_LOCK_ACQUIRE and CPU_LOCK_RELEASE and send out notifications for these in _cpu_up and _cpu_down. This would help us standardise the acquire and release of the subsystem locks in the hotcpu callback functions of these subsystems. [PATCH 3/4] : Eliminate lock_cpu_hotplug from kernel/sched.c. [PATCH 4/4] : In workqueue_cpu_callback function, acquire(release) the workqueue_mutex while handling CPU_LOCK_ACQUIRE(CPU_LOCK_RELEASE). If the per-subsystem-locking approach survives the test of time, we can expect a slow phasing out of lock_cpu_hotplug, which has not yet been eliminated in these patches :) This patch: Provide notifier_call_chain with an option to call only a specified number of notifiers and also record the number of call to notifiers made. The need for this enhancement was identified in the post entitled "Slab - Eliminate lock_cpu_hotplug from slab" (http://lkml.org/lkml/2006/10/28/92) by Ravikiran G Thirumalai and Andrew Morton. This patch adds two additional parameters to notifier_call_chain API namely - int nr_to_calls : Number of notifier_functions to be called. The don't care value is -1. - unsigned int *nr_calls : Records the total number of notifier_funtions called by notifier_call_chain. The don't care value is NULL. Credit: Andrew Morton Signed-off-by: Gautham R Shenoy Signed-off-by: Andrew Morton --- include/linux/notifier.h | 8 +++ kernel/sys.c | 97 ++++++++++++++++++++++++++++++------- 2 files changed, 89 insertions(+), 16 deletions(-) diff -puN include/linux/notifier.h~extend-notifier_call_chain-to-count-nr_calls-made include/linux/notifier.h --- a/include/linux/notifier.h~extend-notifier_call_chain-to-count-nr_calls-made +++ a/include/linux/notifier.h @@ -132,12 +132,20 @@ extern int srcu_notifier_chain_unregiste extern int atomic_notifier_call_chain(struct atomic_notifier_head *, unsigned long val, void *v); +extern int __atomic_notifier_call_chain(struct atomic_notifier_head *, + unsigned long val, void *v, int nr_to_call, unsigned int *nr_calls); extern int blocking_notifier_call_chain(struct blocking_notifier_head *, unsigned long val, void *v); +extern int __blocking_notifier_call_chain(struct blocking_notifier_head *, + unsigned long val, void *v, int nr_to_call, unsigned int *nr_calls); extern int raw_notifier_call_chain(struct raw_notifier_head *, unsigned long val, void *v); +extern int __raw_notifier_call_chain(struct raw_notifier_head *, + unsigned long val, void *v, int nr_to_call, unsigned int *nr_calls); extern int srcu_notifier_call_chain(struct srcu_notifier_head *, unsigned long val, void *v); +extern int __srcu_notifier_call_chain(struct srcu_notifier_head *, + unsigned long val, void *v, int nr_to_call, unsigned int *nr_calls); #define NOTIFY_DONE 0x0000 /* Don't care */ #define NOTIFY_OK 0x0001 /* Suits me */ diff -puN kernel/sys.c~extend-notifier_call_chain-to-count-nr_calls-made kernel/sys.c --- a/kernel/sys.c~extend-notifier_call_chain-to-count-nr_calls-made +++ a/kernel/sys.c @@ -134,19 +134,41 @@ static int notifier_chain_unregister(str return -ENOENT; } +/* + * notifier_call_chain - Informs the registered notifiers about an event. + * + * @nl: Pointer to head of the blocking notifier chain + * @val: Value passed unmodified to notifier function + * @v: Pointer passed unmodified to notifier function + * @nr_to_call: Number of notifier functions to be called. Don't care + * value of this parameter is -1. + * @nr_calls: Records the number of notifications sent. Don't care + * value of this field is NULL. + * + * RETURN VALUE: notifier_call_chain returns the value returned by the + * last notifier function called. + */ + static int __kprobes notifier_call_chain(struct notifier_block **nl, - unsigned long val, void *v) + unsigned long val, void *v, + int nr_to_call, unsigned int *nr_calls) { int ret = NOTIFY_DONE; struct notifier_block *nb, *next_nb; nb = rcu_dereference(*nl); - while (nb) { + + while (nb && nr_to_call) { next_nb = rcu_dereference(nb->next); ret = nb->notifier_call(nb, val, v); + + if (nr_calls) + *nr_calls ++; + if ((ret & NOTIFY_STOP_MASK) == NOTIFY_STOP_MASK) break; nb = next_nb; + nr_to_call--; } return ret; } @@ -205,10 +227,13 @@ int atomic_notifier_chain_unregister(str EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister); /** - * atomic_notifier_call_chain - Call functions in an atomic notifier chain + * __atomic_notifier_call_chain - Call functions in an atomic notifier + * chain * @nh: Pointer to head of the atomic notifier chain * @val: Value passed unmodified to notifier function * @v: Pointer passed unmodified to notifier function + * @nr_to_call: See the comment for notifier_call_chain. + * @nr_calls: See the comment for notifier_call_chain. * * Calls each function in a notifier chain in turn. The functions * run in an atomic context, so they must not block. @@ -222,19 +247,27 @@ EXPORT_SYMBOL_GPL(atomic_notifier_chain_ * of the last notifier function called. */ -int __kprobes atomic_notifier_call_chain(struct atomic_notifier_head *nh, - unsigned long val, void *v) +int __kprobes __atomic_notifier_call_chain(struct atomic_notifier_head *nh, + unsigned long val, void *v, + int nr_to_call, unsigned int *nr_calls) { int ret; rcu_read_lock(); - ret = notifier_call_chain(&nh->head, val, v); + ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls); rcu_read_unlock(); return ret; } -EXPORT_SYMBOL_GPL(atomic_notifier_call_chain); +EXPORT_SYMBOL_GPL(__atomic_notifier_call_chain); +int __kprobes atomic_notifier_call_chain(struct atomic_notifier_head *nh, + unsigned long val, void *v) +{ + return __atomic_notifier_call_chain(nh, val, v, -1, NULL); +} + +EXPORT_SYMBOL_GPL(atomic_notifier_call_chain); /* * Blocking notifier chain routines. All access to the chain is * synchronized by an rwsem. @@ -304,10 +337,13 @@ int blocking_notifier_chain_unregister(s EXPORT_SYMBOL_GPL(blocking_notifier_chain_unregister); /** - * blocking_notifier_call_chain - Call functions in a blocking notifier chain + * __blocking_notifier_call_chain - Call functions in a blocking notifier + * chain * @nh: Pointer to head of the blocking notifier chain * @val: Value passed unmodified to notifier function * @v: Pointer passed unmodified to notifier function + * @nr_to_call: See comment for notifier_call_chain. + * @nr_calls: See comment for notifier_call_chain. * * Calls each function in a notifier chain in turn. The functions * run in a process context, so they are allowed to block. @@ -320,17 +356,26 @@ EXPORT_SYMBOL_GPL(blocking_notifier_chai * of the last notifier function called. */ -int blocking_notifier_call_chain(struct blocking_notifier_head *nh, - unsigned long val, void *v) +int __blocking_notifier_call_chain(struct blocking_notifier_head *nh, + unsigned long val, void *v, + int nr_to_call, unsigned int * nr_calls) { int ret; down_read(&nh->rwsem); - ret = notifier_call_chain(&nh->head, val, v); + ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls); up_read(&nh->rwsem); return ret; } +EXPORT_SYMBOL_GPL(__blocking_notifier_call_chain); + +int blocking_notifier_call_chain(struct blocking_notifier_head *nh, + unsigned long val, void *v) +{ + return __blocking_notifier_call_chain(nh, val, v, -1, NULL); +} + EXPORT_SYMBOL_GPL(blocking_notifier_call_chain); /* @@ -376,10 +421,12 @@ int raw_notifier_chain_unregister(struct EXPORT_SYMBOL_GPL(raw_notifier_chain_unregister); /** - * raw_notifier_call_chain - Call functions in a raw notifier chain + * __raw_notifier_call_chain - Call functions in a raw notifier chain * @nh: Pointer to head of the raw notifier chain * @val: Value passed unmodified to notifier function * @v: Pointer passed unmodified to notifier function + * @nr_to_call: See comment for notifier_call_chain. + * @nr_calls: See comment for notifier_call_chain * * Calls each function in a notifier chain in turn. The functions * run in an undefined context. @@ -393,10 +440,19 @@ EXPORT_SYMBOL_GPL(raw_notifier_chain_unr * of the last notifier function called. */ +int __raw_notifier_call_chain(struct raw_notifier_head *nh, + unsigned long val, void *v, + int nr_to_call, unsigned int *nr_calls) +{ + return notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls); +} + +EXPORT_SYMBOL_GPL(__raw_notifier_call_chain); + int raw_notifier_call_chain(struct raw_notifier_head *nh, unsigned long val, void *v) { - return notifier_call_chain(&nh->head, val, v); + return __raw_notifier_call_chain(nh, val, v, -1, NULL); } EXPORT_SYMBOL_GPL(raw_notifier_call_chain); @@ -475,6 +531,8 @@ EXPORT_SYMBOL_GPL(srcu_notifier_chain_un * @nh: Pointer to head of the SRCU notifier chain * @val: Value passed unmodified to notifier function * @v: Pointer passed unmodified to notifier function + * @nr_to_call: See comment for notifier_call_chain. + * @nr_calls: See comment for notifier_call_chain * * Calls each function in a notifier chain in turn. The functions * run in a process context, so they are allowed to block. @@ -487,18 +545,25 @@ EXPORT_SYMBOL_GPL(srcu_notifier_chain_un * of the last notifier function called. */ -int srcu_notifier_call_chain(struct srcu_notifier_head *nh, - unsigned long val, void *v) +int __srcu_notifier_call_chain(struct srcu_notifier_head *nh, + unsigned long val, void *v, + int nr_to_call, unsigned int *nr_calls) { int ret; int idx; idx = srcu_read_lock(&nh->srcu); - ret = notifier_call_chain(&nh->head, val, v); + ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls); srcu_read_unlock(&nh->srcu, idx); return ret; } +EXPORT_SYMBOL_GPL(__srcu_notifier_call_chain); +int srcu_notifier_call_chain(struct srcu_notifier_head *nh, + unsigned long val, void *v) +{ + return __srcu_notifier_call_chain(nh, val, v, -1, NULL); +} EXPORT_SYMBOL_GPL(srcu_notifier_call_chain); /** _