linux-kernel - Re: [PATCH 0/3] extend get/setrlimit to support setting rlimits external to a process (v7)

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Message-ID: <20091109164053.GB5160@redhat.com>
Date:	Mon, 9 Nov 2009 17:40:53 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Neil Horman <nhorman@...driver.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	marcin.slusarz@...il.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/3] extend get/setrlimit to support setting rlimits
	external to a process (v7)

On 11/09, Jiri Slaby wrote:
>
> +	ppid = find_get_pid(pid);
> +	if (!ppid)
> +		goto out;
> +
> +	tsk = get_pid_task(ppid, PIDTYPE_PID);
> +
> +	if (!tsk)
> +		goto out_put_pid;
> +
> +	if (resource >= RLIM_NLIMITS)
> +		goto out_put_all;
> +
> +	retval = -EBUSY;
> +	if (!lock_task_sighand(tsk, &flags))
>
> X task_lock below cannot nest inside sighand (according to Oleg)

Yes, this is deadlockable.

Also, I don't understand why wthis code get's both pid and task_struct().

And the "if (resource >= RLIM_NLIMITS)" check is racy afaics, see
http://marc.info/?l=linux-kernel&m=125200862124872

Oleg.

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