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Subject[patch resend 2/2] oprofile: simplify task handoff
Since the task handoff notifier is isolated only to oprofile, it no
longer consists of a possible chain of notifiers. Thus, it's easy to
replace it with a simple linked list when enabled, which is anytime that
the notifier would have been registered.

Signed-off-by: David Rientjes <rientjes@google.com>
---
resend: no response to first posting on Nov 14

drivers/oprofile/buffer_sync.c | 68 ++++++++++++++--------------------------
1 file changed, 23 insertions(+), 45 deletions(-)

diff --git a/drivers/oprofile/buffer_sync.c b/drivers/oprofile/buffer_sync.c
--- a/drivers/oprofile/buffer_sync.c
+++ b/drivers/oprofile/buffer_sync.c
@@ -42,24 +42,7 @@ static LIST_HEAD(dead_tasks);
static cpumask_var_t marked_cpus;
static DEFINE_SPINLOCK(task_mortuary);
static void process_task_mortuary(void);
-static ATOMIC_NOTIFIER_HEAD(task_free_notifier);
-
-static int task_handoff_register(struct notifier_block *n)
-{
- return atomic_notifier_chain_register(&task_free_notifier, n);
-}
-
-static int task_handoff_unregister(struct notifier_block *n)
-{
- return atomic_notifier_chain_unregister(&task_free_notifier, n);
-}
-
-int profile_handoff_task(struct task_struct *task)
-{
- int ret;
- ret = atomic_notifier_call_chain(&task_free_notifier, 0, task);
- return (ret == NOTIFY_OK) ? 1 : 0;
-}
+static bool task_handoff_enabled __read_mostly;

/* Take ownership of the task struct and place it on the
* list for processing. Only after two full buffer syncs
@@ -68,15 +51,17 @@ int profile_handoff_task(struct task_struct *task)
* Can be invoked from softirq via RCU callback due to
* call_rcu() of the task struct, hence the _irqsave.
*/
-static int
-task_free_notify(struct notifier_block *self, unsigned long val, void *data)
+int profile_handoff_task(struct task_struct *task)
{
unsigned long flags;
- struct task_struct *task = data;
- spin_lock_irqsave(&task_mortuary, flags);
- list_add(&task->tasks, &dying_tasks);
- spin_unlock_irqrestore(&task_mortuary, flags);
- return NOTIFY_OK;
+
+ if (task_handoff_enabled) {
+ spin_lock_irqsave(&task_mortuary, flags);
+ list_add(&task->tasks, &dying_tasks);
+ spin_unlock_irqrestore(&task_mortuary, flags);
+ return 1;
+ }
+ return 0;
}


@@ -143,10 +128,6 @@ module_load_notify(struct notifier_block *self, unsigned long val, void *data)
}


-static struct notifier_block task_free_nb = {
- .notifier_call = task_free_notify,
-};
-
static struct notifier_block task_exit_nb = {
.notifier_call = task_exit_notify,
};
@@ -173,33 +154,30 @@ int sync_start(void)
if (!zalloc_cpumask_var(&marked_cpus, GFP_KERNEL))
return -ENOMEM;

- err = task_handoff_register(&task_free_nb);
- if (err)
- goto out1;
+ task_handoff_enabled = true;
+ barrier();
err = profile_event_register(PROFILE_TASK_EXIT, &task_exit_nb);
if (err)
- goto out2;
+ goto out1;
err = profile_event_register(PROFILE_MUNMAP, &munmap_nb);
if (err)
- goto out3;
+ goto out2;
err = register_module_notifier(&module_load_nb);
if (err)
- goto out4;
+ goto out3;

start_cpu_work();
-
-out:
- return err;
-out4:
- profile_event_unregister(PROFILE_MUNMAP, &munmap_nb);
+ return 0;
out3:
- profile_event_unregister(PROFILE_TASK_EXIT, &task_exit_nb);
+ profile_event_unregister(PROFILE_MUNMAP, &munmap_nb);
out2:
- task_handoff_unregister(&task_free_nb);
- free_all_tasks();
+ profile_event_unregister(PROFILE_TASK_EXIT, &task_exit_nb);
out1:
+ task_handoff_enabled = false;
+ barrier();
+ free_all_tasks();
free_cpumask_var(marked_cpus);
- goto out;
+ return err;
}


@@ -209,7 +187,7 @@ void sync_stop(void)
unregister_module_notifier(&module_load_nb);
profile_event_unregister(PROFILE_MUNMAP, &munmap_nb);
profile_event_unregister(PROFILE_TASK_EXIT, &task_exit_nb);
- task_handoff_unregister(&task_free_nb);
+ task_handoff_enabled = false;
barrier(); /* do all of the above first */

flush_cpu_work();

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