linux-kernel - Re: [PATCH 5/5] Move alloc_pid call to copy

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Message-ID: <20070715123600.GA210@tv-sign.ru>
Date:	Sun, 15 Jul 2007 16:36:00 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Sukadev Bhattiprolu <sukadev@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Cedric Le Goater <clg@...ibm.com>,
	Dave Hansen <haveblue@...ibm.com>,
	Serge Hallyn <serue@...ibm.com>,
	Herbert Poetzel <herbert@...hfloor.at>,
	Pavel Emelianov <xemul@...nvz.org>,
	Linux Containers <containers@...ts.osdl.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] Move alloc_pid call to copy_process

Sukadev Bhattiprolu wrote:
>
> --- lx26-22-rc6-mm1.orig/kernel/pid.c	2007-07-13 18:23:55.000000000 -0700
> +++ lx26-22-rc6-mm1/kernel/pid.c	2007-07-13 18:23:55.000000000 -0700
> @@ -206,6 +206,10 @@ fastcall void free_pid(struct pid *pid)
>  	/* We can be called with write_lock_irq(&tasklist_lock) held */
>  	unsigned long flags;
>  
> +	/* check this here to keep copy_process() cleaner */
> +	if (unlikely(pid == &init_struct_pid))
> +		return;
> +
>  	spin_lock_irqsave(&pidmap_lock, flags);
>  	hlist_del_rcu(&pid->pid_chain);
>  	spin_unlock_irqrestore(&pidmap_lock, flags);
> @@ -214,13 +218,17 @@ fastcall void free_pid(struct pid *pid)
>  	call_rcu(&pid->rcu, delayed_put_pid);
>  }
>  
> -struct pid *alloc_pid(void)
> +struct pid *alloc_pid(enum copy_process_type copy_src)
>  {
>  	struct pid *pid;
>  	enum pid_type type;
>  	int nr = -1;
>  	struct pid_namespace *ns;
>  
> +	/* check this here to keep copy_process() cleaner */
> +	if (unlikely(copy_src == COPY_IDLE_PROCESS))
> +		return &init_struct_pid;
> +
>  	ns = task_active_pid_ns(current);
>  	pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
>  	if (!pid)

Ugh. I am sorry! but imho this is so ugly :(

Could you please give more details why we need this change? Even if we really
need this, can't we do these checks in copy_process() ? free_pid(&init_struct_pid)
can only happen when fork fails, this is a slow path, and copy_process() knows
copy_src.

Oleg.

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