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Commit 36b2f046 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Thomas Gleixner
Browse files

posix-timers: sys_timer_create: simplify and s/tasklist/rcu/ 



- Change the code to do rcu_read_lock() instead of taking tasklist_lock,
  it is safe to get_task_struct(p) if p was found under RCU.

  However, now we must not use process's sighand/signal, they may be NULL.
  We can use current->sighand/signal instead, this "process" must belong
  to the current's thread-group.

- Factor out the common code for 2 "if (timer_event_spec)" branches, the
  !timer_event_spec case can use current too.

- use spin_lock_irq() instead of _irqsave(), kill "flags".

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Cc: mingo@elte.hu
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 2cd499e3

kernel/posix-timers.c

+8 −15
Original line number Diff line number Diff line
@@ -463,7 +463,6 @@ sys_timer_create(const clockid_t which_clock, 
	struct k_itimer *new_timer;

	int new_timer_id;

	struct task_struct *process;

	unsigned long flags;

	sigevent_t event;

	int it_id_set = IT_ID_NOT_SET;
@@ -521,16 +520,11 @@ sys_timer_create(const clockid_t which_clock, 
		new_timer->it_sigev_signo = event.sigev_signo;

		new_timer->it_sigev_value = event.sigev_value;



		read_lock(&tasklist_lock);

		if ((process = good_sigevent(&event))) {

		rcu_read_lock();

		process = good_sigevent(&event);

		if (process)

			get_task_struct(process);

			spin_lock_irqsave(&process->sighand->siglock, flags);

			new_timer->it_process = process;

			list_add(&new_timer->list,

				&process->signal->posix_timers);

			spin_unlock_irqrestore(&process->sighand->siglock, flags);

		}

		read_unlock(&tasklist_lock);

		rcu_read_unlock();

		if (!process) {

			error = -EINVAL;

			goto out;
@@ -541,19 +535,18 @@ sys_timer_create(const clockid_t which_clock, 
		new_timer->it_sigev_value.sival_int = new_timer->it_id;

		process = current->group_leader;

		get_task_struct(process);

		spin_lock_irqsave(&process->sighand->siglock, flags);

		new_timer->it_process = process;

		list_add(&new_timer->list, &process->signal->posix_timers);

		spin_unlock_irqrestore(&process->sighand->siglock, flags);

	}



	spin_lock_irq(&current->sighand->siglock);

	new_timer->it_process = process;

	list_add(&new_timer->list, &current->signal->posix_timers);

	spin_unlock_irq(&current->sighand->siglock);

 	/*

	 * In the case of the timer belonging to another task, after

	 * the task is unlocked, the timer is owned by the other task

	 * and may cease to exist at any time.  Don't use or modify

	 * new_timer after the unlock call.

	 */



out:

	if (error)

		release_posix_timer(new_timer, it_id_set);