linux-kernel - Re: [PATCH] staging: android/lowmemorykiller: Don't grab tasklist

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Date:	Thu, 2 Feb 2012 13:54:41 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
Cc:	Greg KH <gregkh@...e.de>,
	Arve Hjønnevåg <arve@...roid.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	San Mehat <san@...gle.com>, Colin Cross <ccross@...roid.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com,
	linaro-kernel@...ts.linaro.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] staging: android/lowmemorykiller: Don't grab
	tasklist_lock

On 02/01, Anton Vorontsov wrote:
>
> @@ -132,7 +133,7 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
>  	}
>  	selected_oom_adj = min_adj;
>
> -	read_lock(&tasklist_lock);
> +	rcu_read_lock();

This has the same problem, force_sig() becomes unsafe.

Why do you need force_? Do you really want to kill /sbin/init (or sub-namespace
init) ?

We could change force_sig_info() to use lock_task_sighand(), but I'd like to
avoid this. Imho, this interface should be cleanuped, and it should be used
for synchronous signals only.

With or without this patch, sig == NULL is not possible but !mm is not right,
there could be other other threads with mm != NULL.

Oleg.

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