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SubjectRe: [PATCH 1/4] add task handling notifier: base definitions
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On Thu, 2007-12-20 at 13:12 +0000, Jan Beulich wrote:
> This is the base patch, adding notification for task creation and
> deletion.
>
> Signed-off-by: Jan Beulich <jbeulich@novell.com>
> ---
> include/linux/sched.h | 8 +++++++-
> kernel/fork.c | 11 +++++++++++
> 2 files changed, 18 insertions(+), 1 deletion(-)
>
> --- 2.6.24-rc5-notify-task.orig/include/linux/sched.h
> +++ 2.6.24-rc5-notify-task/include/linux/sched.h
> @@ -80,7 +80,7 @@ struct sched_param {
> #include <linux/rcupdate.h>
> #include <linux/futex.h>
> #include <linux/rtmutex.h>
> -
> +#include <linux/notifier.h>
> #include <linux/time.h>
> #include <linux/param.h>
> #include <linux/resource.h>
> @@ -1700,6 +1700,12 @@ extern int do_execve(char *, char __user
> extern long do_fork(unsigned long, unsigned long, struct pt_regs *, unsigned long, int __user *, int __user *);
> struct task_struct *fork_idle(int);
>
> +#define TASK_NEW 1
> +#define TASK_DELETE 2
> +
> +extern struct blocking_notifier_head task_notifier_list;
> +extern struct atomic_notifier_head atomic_task_notifier_list;
> +
> extern void set_task_comm(struct task_struct *tsk, char *from);
> extern void get_task_comm(char *to, struct task_struct *tsk);
>
> --- 2.6.24-rc5-notify-task.orig/kernel/fork.c
> +++ 2.6.24-rc5-notify-task/kernel/fork.c
> @@ -46,6 +46,7 @@
> #include <linux/tsacct_kern.h>
> #include <linux/cn_proc.h>
> #include <linux/freezer.h>
> +#include <linux/notifier.h>
> #include <linux/delayacct.h>
> #include <linux/taskstats_kern.h>
> #include <linux/random.h>
> @@ -71,6 +72,11 @@ DEFINE_PER_CPU(unsigned long, process_co
>
> __cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */
>
> +BLOCKING_NOTIFIER_HEAD(task_notifier_list);
> +EXPORT_SYMBOL_GPL(task_notifier_list);
> +ATOMIC_NOTIFIER_HEAD(atomic_task_notifier_list);
> +EXPORT_SYMBOL_GPL(atomic_task_notifier_list);
> +

When these global notifier lists were proposed years ago folks at SGI
loudly objected with concerns over anticipated cache line bouncing on
512+ cpu machines. Is that no longer a concern?

> int nr_processes(void)
> {
> int cpu;
> @@ -121,6 +127,9 @@ void __put_task_struct(struct task_struc
> WARN_ON(atomic_read(&tsk->usage));
> WARN_ON(tsk == current);
>
> + atomic_notifier_call_chain(&atomic_task_notifier_list,
> + TASK_DELETE, tsk);
> +
> security_task_free(tsk);
> free_uid(tsk->user);
> put_group_info(tsk->group_info);

Would the atomic notifier call chain be necessary if you hooked into an
earlier section of do_exit() instead?

Cheers,
-Matt Helsley



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