Re: [PATCH 2/8] mm/oom_kill: convert process/thread iterators to for_each_*_rcu

[Michal Hocko]

On Fri 04-09-26 16:29:54, Ye Liu wrote:
> From: Ye Liu <liuye@xxxxxxxxxx>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() pairs wrapping
> for_each_process()/for_each_thread() loops with for_each_process_rcu()
> and for_each_thread_rcu(), so that the RCU read-side critical section
> is scoped to the loop body.
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@xxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  mm/oom_kill.c | 20 +++++---------------
>  1 file changed, 5 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 5f372f6e26fa..8dd025965810 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -94,8 +94,7 @@ static bool oom_cpuset_eligible(struct task_struct *start,
>  	bool ret = false;
>  	const nodemask_t *mask = oc->nodemask;
>  
> -	rcu_read_lock();
> -	for_each_thread(start, tsk) {
> +	for_each_thread_rcu(start, tsk) {
>  		if (mask) {
>  			/*
>  			 * If this is a mempolicy constrained oom, tsk's
> @@ -114,7 +113,6 @@ static bool oom_cpuset_eligible(struct task_struct *start,
>  		if (ret)
>  			break;
>  	}
> -	rcu_read_unlock();
>  
>  	return ret;
>  }
> @@ -368,11 +366,9 @@ static void select_bad_process(struct oom_control *oc)
>  	else {
>  		struct task_struct *p;
>  
> -		rcu_read_lock();
> -		for_each_process(p)
> +		for_each_process_rcu(p)
>  			if (oom_evaluate_task(p, oc))
>  				break;
> -		rcu_read_unlock();
>  	}
>  }
>  
> @@ -430,14 +426,12 @@ static void dump_tasks(struct oom_control *oc)
>  		struct task_struct *p;
>  		int i = 0;
>  
> -		rcu_read_lock();
> -		for_each_process(p) {
> +		for_each_process_rcu(p) {
>  			/* Avoid potential softlockup warning */
>  			if ((++i & 1023) == 0)
>  				touch_softlockup_watchdog();
>  			dump_task(p, oc);
>  		}
> -		rcu_read_unlock();
>  	}
>  }
>  
> @@ -894,8 +888,7 @@ static bool task_will_free_mem(struct task_struct *task)
>  	 * are dying as well to make sure that a) nobody pins its mm and
>  	 * b) the task is also reapable by the oom reaper.
>  	 */
> -	rcu_read_lock();
> -	for_each_process(p) {
> +	for_each_process_rcu(p) {
>  		if (!process_shares_mm(p, mm))
>  			continue;
>  		if (same_thread_group(task, p))
> @@ -904,7 +897,6 @@ static bool task_will_free_mem(struct task_struct *task)
>  		if (!ret)
>  			break;
>  	}
> -	rcu_read_unlock();
>  
>  	return ret;
>  }
> @@ -960,8 +952,7 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
>  	 * That thread will now get access to memory reserves since it has a
>  	 * pending fatal signal.
>  	 */
> -	rcu_read_lock();
> -	for_each_process(p) {
> +	for_each_process_rcu(p) {
>  		if (!process_shares_mm(p, mm))
>  			continue;
>  		if (same_thread_group(p, victim))
> @@ -982,7 +973,6 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
>  			continue;
>  		do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID);
>  	}
> -	rcu_read_unlock();
>  
>  	if (can_oom_reap)
>  		queue_oom_reaper(victim);
> -- 
> 2.25.1

-- 
Michal Hocko
SUSE Labs