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

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- 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: Oleg Nesterov <oleg@tv-sign.ru>
Cc: mingo@elte.hu
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Oleg Nesterov 2008-09-22 14:42:48 -07:00 committed by Thomas Gleixner
parent 2cd499e38e
commit 36b2f04600
1 changed files with 8 additions and 15 deletions
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23
kernel/posix-timers.c
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@ -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);