linux-kernel - Re: [BUGFIX v2] memcg: fix res_counter_read_u64 lock aware (Was Re: [PATCH] oom: handle overflow in mem_cgroup_out_of

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Message-Id: <20110126175722.01b0db3a.akpm@linux-foundation.org>
Date:	Wed, 26 Jan 2011 17:57:22 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Greg Thelen <gthelen@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUGFIX v2] memcg: fix res_counter_read_u64 lock aware (Was Re:
 [PATCH] oom: handle overflow in mem_cgroup_out_of_memory()

On Thu, 27 Jan 2011 10:43:39 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> --- mmotm-0125.orig/kernel/res_counter.c
> +++ mmotm-0125/kernel/res_counter.c
> @@ -126,10 +126,24 @@ ssize_t res_counter_read(struct res_coun
>  			pos, buf, s - buf);
>  }
>  
> +#if BITS_PER_LONG == 32
> +u64 res_counter_read_u64(struct res_counter *counter, int member)
> +{
> +	unsigned long flags;
> +	u64 ret;
> +
> +	spin_lock_irqsave(&counter->lock, flags);
> +	ret = *res_counter_member(counter, member);
> +	spin_unlock_irqrestore(&counter->lock, flags);
> +
> +	return ret;
> +}
> +#else
>  u64 res_counter_read_u64(struct res_counter *counter, int member)
>  {
>  	return *res_counter_member(counter, member);
>  }
> +#endif

_irqsave is only needed if the lock will be taken from irq context. 
Does that happen?

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