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Subject[PATCH 2/4] 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: Oleg Nesterov <oleg@tv-sign.ru>

--- 26-rc2/kernel/posix-timers.c~5_CLEANUP 2008-08-04 16:50:29.000000000 +0400
+++ 26-rc2/kernel/posix-timers.c 2008-08-04 18:13:10.000000000 +0400
@@ -463,7 +463,6 @@ sys_timer_create(const clockid_t which_c
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_c
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_c
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);


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