linux-kernel - Re: [PATCH] pids: introduce find_get_task_by

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Message-ID: <20171026135825.GA16528@redhat.com>
Date:   Thu, 26 Oct 2017 15:58:25 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Darren Hart <dvhart@...radead.org>,
        Balbir Singh <bsingharora@...il.com>,
        linux-mm <linux-mm@...ck.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pids: introduce find_get_task_by_vpid helper

On 10/26, Mike Rapoport wrote:
>
> There are several functions that do find_task_by_vpid() followed by
> get_task_struct(). We can use a helper function instead.

Yes, agreed, I was going to do this many times.

> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -870,12 +870,7 @@ static struct task_struct *futex_find_get_task(pid_t pid)
>  {
>  	struct task_struct *p;
>  
> -	rcu_read_lock();
> -	p = find_task_by_vpid(pid);
> -	if (p)
> -		get_task_struct(p);
> -
> -	rcu_read_unlock();
> +	p = find_get_task_by_vpid(pid);
>  
>  	return p;

OK, but then I think you should remove futex_find_get_task() and convert
it callers to use the new helper.

> @@ -1103,11 +1103,7 @@ static struct task_struct *ptrace_get_task_struct(pid_t pid)
>  {
>  	struct task_struct *child;
>  
> -	rcu_read_lock();
> -	child = find_task_by_vpid(pid);
> -	if (child)
> -		get_task_struct(child);
> -	rcu_read_unlock();
> +	child = find_get_task_by_vpid(pid);
>  
>  	if (!child)
>  		return ERR_PTR(-ESRCH);

The same. ptrace_get_task_struct() should die imo.

Oleg.