Re: [PATCH] mm/oom_kill: simplify remaining RCU sections with guard(rcu)

[Michal Hocko]

On Thu 13-08-26 11:26:33, Ye Liu wrote:
> From: Ye Liu <liuye@xxxxxxxxxx>
> 
> Replace the remaining manual rcu_read_lock()/rcu_read_unlock() pairs
> in oom_cpuset_eligible(), select_bad_process(), dump_tasks(),
> task_will_free_mem(), and __oom_kill_process() with guard(rcu)() for
> consistency and simpler control flow.

Could you use scoped_guard instead? While all these functions do not
perform anything pas the for loop this might change in the future and I
find it more obvious what the actual scope for the RCU is rather than
the full function one.
> 
> Signed-off-by: Ye Liu <liuye@xxxxxxxxxx>
> ---
>  mm/oom_kill.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 4b5c70aaece4..8bbb5ca00bb6 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -94,7 +94,7 @@ static bool oom_cpuset_eligible(struct task_struct *start,
>  	bool ret = false;
>  	const nodemask_t *mask = oc->nodemask;
>  
> -	rcu_read_lock();
> +	guard(rcu)();
>  	for_each_thread(start, tsk) {
>  		if (mask) {
>  			/*
> @@ -114,7 +114,6 @@ static bool oom_cpuset_eligible(struct task_struct *start,
>  		if (ret)
>  			break;
>  	}
> -	rcu_read_unlock();
>  
>  	return ret;
>  }
> @@ -368,11 +367,10 @@ static void select_bad_process(struct oom_control *oc)
>  	else {
>  		struct task_struct *p;
>  
> -		rcu_read_lock();
> +		guard(rcu)();
>  		for_each_process(p)
>  			if (oom_evaluate_task(p, oc))
>  				break;
> -		rcu_read_unlock();
>  	}
>  }
>  
> @@ -430,14 +428,13 @@ static void dump_tasks(struct oom_control *oc)
>  		struct task_struct *p;
>  		int i = 0;
>  
> -		rcu_read_lock();
> +		guard(rcu)();
>  		for_each_process(p) {
>  			/* Avoid potential softlockup warning */
>  			if ((++i & 1023) == 0)
>  				touch_softlockup_watchdog();
>  			dump_task(p, oc);
>  		}
> -		rcu_read_unlock();
>  	}
>  }
>  
> @@ -894,7 +891,7 @@ 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();
> +	guard(rcu)();
>  	for_each_process(p) {
>  		if (!process_shares_mm(p, mm))
>  			continue;
> @@ -904,7 +901,6 @@ static bool task_will_free_mem(struct task_struct *task)
>  		if (!ret)
>  			break;
>  	}
> -	rcu_read_unlock();
>  
>  	return ret;
>  }
> @@ -960,7 +956,7 @@ 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();
> +	guard(rcu)();
>  	for_each_process(p) {
>  		if (!process_shares_mm(p, mm))
>  			continue;
> @@ -982,7 +978,6 @@ 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