linux-kernel - Re: [PATCH] do_fork(): Rename 'stack_size' argument to reflect actual use

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Message-ID: <alpine.DEB.2.10.1503041505550.25790@chino.kir.corp.google.com>
Date:	Wed, 4 Mar 2015 15:07:45 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Alex Dowad <alexinbeijing@...il.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Kees Cook <keescook@...omium.org>,
	Aaron Tomlin <atomlin@...hat.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] do_fork(): Rename 'stack_size' argument to reflect actual
 use

On Wed, 4 Mar 2015, Alex Dowad wrote:

> The 'stack_size' argument is never used to pass a stack size. It's only used when
> forking a kernel thread, in which case it is an argument which should be passed
> to the 'main' function which the kernel thread executes. Hence, rename it to
> 'kthread_arg'.
> 
> Signed-off-by: Alex Dowad <alexinbeijing@...il.com>
> ---
> 
> Hi,
> 
> Please have a look at this patch. If this is accepted, I have a series of patches
> ready for a similar cleanup to all the arch-specific implementations of copy_thread()
> (as suggested by Andrew Morton in a private e-mail).
> 
> Thank you,
> Alex Dowad
> 
>  kernel/fork.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index cf65139..b38a2ae 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1186,10 +1186,12 @@ init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
>   * It copies the registers, and all the appropriate
>   * parts of the process environment (as per the clone
>   * flags). The actual kick-off is left to the caller.
> + *
> + * When copying a kernel thread, 'stack_start' is the function to run.
>   */
>  static struct task_struct *copy_process(unsigned long clone_flags,
>  					unsigned long stack_start,
> -					unsigned long stack_size,
> +					unsigned long kthread_arg,
>  					int __user *child_tidptr,
>  					struct pid *pid,
>  					int trace)
> @@ -1401,7 +1403,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  	retval = copy_io(clone_flags, p);
>  	if (retval)
>  		goto bad_fork_cleanup_namespaces;
> -	retval = copy_thread(clone_flags, stack_start, stack_size, p);
> +	retval = copy_thread(clone_flags, stack_start, kthread_arg, p);
>  	if (retval)
>  		goto bad_fork_cleanup_io;
>  
> @@ -1629,8 +1631,8 @@ struct task_struct *fork_idle(int cpu)
>   * it and waits for it to finish using the VM if required.
>   */
>  long do_fork(unsigned long clone_flags,
> -	      unsigned long stack_start,
> -	      unsigned long stack_size,
> +	      unsigned long stack_start, /* or function for kthread to run */
> +	      unsigned long kthread_arg,
>  	      int __user *parent_tidptr,
>  	      int __user *child_tidptr)
>  {

Looks fine, but I'm not sure about commenting functional formals.  Since 
copy_process() and do_fork() can have formals with different meanings, 
then why not just rename them "arg1" and "arg2" respectively and then 
define in the comment above the function what the possible combinations 
are?

> @@ -1656,7 +1658,7 @@ long do_fork(unsigned long clone_flags,
>  			trace = 0;
>  	}
>  
> -	p = copy_process(clone_flags, stack_start, stack_size,
> +	p = copy_process(clone_flags, stack_start, kthread_arg,
>  			 child_tidptr, NULL, trace);
>  	/*
>  	 * Do this prior waking up the new thread - the thread pointer
> @@ -1740,7 +1742,7 @@ SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
>  		 int, tls_val)
>  #elif defined(CONFIG_CLONE_BACKWARDS3)
>  SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
> -		int, stack_size,
> +		int, ignored,
>  		int __user *, parent_tidptr,
>  		int __user *, child_tidptr,
>  		int, tls_val)
--
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