linux-kernel - Re: [PATCH 1/2] break out page allocation warning code

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Date:	Wed, 20 Apr 2011 11:19:52 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Stultz <johnstul@...ibm.com>
Subject: Re: [PATCH 1/2] break out page allocation warning code

> The concept is ok to me. but AFAIK some caller are now using ARRAY_SIZE(tsk->comm).
> or sizeof(tsk->comm). Probably callers need to be changed too.

one more correction.

>  void set_task_comm(struct task_struct *tsk, char *buf)
>  {
> +	char tmp_comm[TASK_COMM_LEN];
> +
>  	task_lock(tsk);
>  
> +	memcpy(tmp_comm, tsk->comm_buf, TASK_COMM_LEN);
> +	tsk->comm = tmp;
>  	/*
> -	 * Threads may access current->comm without holding
> -	 * the task lock, so write the string carefully.
> -	 * Readers without a lock may see incomplete new
> -	 * names but are safe from non-terminating string reads.
> +	 * Make sure no one is still looking at tsk->comm_buf
>  	 */
> -	memset(tsk->comm, 0, TASK_COMM_LEN);
> -	wmb();
> -	strlcpy(tsk->comm, buf, sizeof(tsk->comm));
> +	synchronize_rcu();

The doc says,

/**
 * synchronize_rcu - wait until a grace period has elapsed.
 *

And here is under spinlock.



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