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 <akpm@osdl.org>
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 77 insertions, 17 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index 8ecfe3473779..d4985df21b60 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);
 
 /**