linux-kernel - Re: Add all thread stats for TASKSTATS_CMD_ATTR

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Message-ID: <20070918152941.GA177@tv-sign.ru>
Date:	Tue, 18 Sep 2007 19:29:41 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Guillaume Chazarain <guichaz@...oo.fr>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	balbir@...ux.vnet.ibm.com, Jonathan Lim <jlim@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jay Lan <jlan@...ulhu.engr.sgi.com>
Subject: Re: Add all thread stats for TASKSTATS_CMD_ATTR_TGID (v5)

On 09/18, Guillaume Chazarain wrote:
>
> @@ -508,7 +543,7 @@ void taskstats_exit(struct task_struct *
>  	if (!stats)
>  		goto err;
>  
> -	memcpy(stats, tsk->signal->stats, sizeof(*stats));
> +	fill_tgid(tsk->pid, tsk, stats);

No, no, this is wrong.

tsk->signal->stats contains the accumulated info about the already exited
threads, we shouldn't throw it out.

Also, fill_tgid() doesn't make sense here, current is the last live sub-thread.

Hmm. We have another race here. There is no guarantee that tsk->signal->stats
covers all sub-threads, as it is supposed to be. It is quite possible that
another sub-thread decremented ->signal->live before us, but didn't complete
taskstats_exit()->fill_tgid_exit() yet.

Oleg.

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