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

[Alex Dowad]

On 05/03/15 01:07, David Rientjes wrote:
> 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@xxxxxxxxx>
> > ---
> >
> > 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?

The second argument is *only* ever used for one thing: an argument 
passed to a kernel thread. That's why I would like to rename it to 
"kthread_arg". The previous argument (currently named "stack_start") is 
indeed used for 2 different things: a new stack pointer for a user 
thread, or a function to be executed by a kernel thread. Rather than 
"arg1", what would you think of something like "sp_or_fn", or "usp_or_fn"?

Thanks for your feedback!

> > @@ -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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