linux-kernel - Re: 2.6.26-rc4: RIP find_pid

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Date:	Wed, 28 May 2008 01:26:50 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: 2.6.26-rc4: RIP find_pid_ns+0x6b/0xa0

On Tue, May 27, 2008 at 09:37:11PM +0400, Oleg Nesterov wrote:
> On 05/27, Oleg Nesterov wrote:
> > But I agree, this race is pretty much theoretical.
> 
> Perhaps we have the unbalanced put_pid(), in that case "struct pid" will
> be freed without waiting for a grace period.
> 
> Alexey, could you re-test with the patch below?

OK, and this is first time I saw this oops.

> --- MM/kernel/pid.c~	2008-02-20 18:29:40.000000000 +0300
> +++ MM/kernel/pid.c	2008-02-20 18:35:15.000000000 +0300
> @@ -208,6 +208,10 @@ void put_pid(struct pid *pid)
>  	ns = pid->numbers[pid->level].ns;
>  	if ((atomic_read(&pid->count) == 1) ||
>  	     atomic_dec_and_test(&pid->count)) {
> +		int type = PIDTYPE_MAX;
> +		while (--type >= 0)
> +			if (WARN_ON(!hlist_empty(&pid->tasks[type])))
> +				return;
>  		kmem_cache_free(ns->pid_cachep, pid);
>  		put_pid_ns(ns);
>  	}

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