From 6f7cc11aa6c7d5002e16096c7590944daece70ed Mon Sep 17 00:00:00 2001 From: Gautham R Shenoy Date: Wed, 9 May 2007 02:34:02 -0700 Subject: Extend notifier_call_chain to count nr_calls made 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. [michal.k.k.piotrowski@gmail.com: build fix] Credit: Andrew Morton Signed-off-by: Gautham R Shenoy Signed-off-by: Michal Piotrowski Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/sys.c | 94 +++++++++++++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 77 insertions(+), 17 deletions(-) (limited to 'kernel/sys.c') diff --git a/kernel/sys.c b/kernel/sys.c index 8ecfe347377..d4985df21b6 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -134,19 +134,39 @@ static int notifier_chain_unregister(struct notifier_block **nl, 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. + * @returns: 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, 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 +225,12 @@ int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh, 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 +244,27 @@ EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister); * 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, 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 +334,12 @@ int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh, 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. @@ -320,8 +352,9 @@ EXPORT_SYMBOL_GPL(blocking_notifier_chain_unregister); * 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, int *nr_calls) { int ret = NOTIFY_DONE; @@ -332,12 +365,19 @@ int blocking_notifier_call_chain(struct blocking_notifier_head *nh, */ if (rcu_dereference(nh->head)) { 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); /* @@ -383,10 +423,12 @@ int raw_notifier_chain_unregister(struct raw_notifier_head *nh, 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. @@ -400,10 +442,19 @@ EXPORT_SYMBOL_GPL(raw_notifier_chain_unregister); * 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, 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); @@ -478,10 +529,12 @@ int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh, EXPORT_SYMBOL_GPL(srcu_notifier_chain_unregister); /** - * srcu_notifier_call_chain - Call functions in an SRCU notifier chain + * __srcu_notifier_call_chain - Call functions in an SRCU notifier chain * @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. @@ -494,18 +547,25 @@ EXPORT_SYMBOL_GPL(srcu_notifier_chain_unregister); * 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, 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); /** -- cgit v1.2.3