linux-kernel - Re: [PATCH 4/5] proc: simpler iterations for /proc/*/cmdline

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Date:   Fri, 20 Apr 2018 22:46:28 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] proc: simpler iterations for /proc/*/cmdline

On Thu, Apr 19, 2018 at 05:15:20PM -0700, Andrew Morton wrote:
> On Wed, 21 Feb 2018 22:30:09 +0300 Alexey Dobriyan <adobriyan@...il.com> wrote:
> 
> > "rv" variable is used both as a counter of bytes transferred and
> > an error value holder but it can be reduced solely to error values
> > if original start of userspace buffer is stashed and used at the very
> > end.
> > 
> > ...
> >
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> >
> > ...
> >
> > @@ -371,12 +365,16 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
> >  		}
> >  	}
> >  
> > +end:
> > +	free_page((unsigned long)page);
> > +	mmput(mm);
> > +	*pos += buf - buf0;
> > +	return buf - buf0;
> > +
> >  out_free_page:
> >  	free_page((unsigned long)page);
> >  out_mmput:
> >  	mmput(mm);
> > -	if (rv > 0)
> > -		*pos += rv;
> >  	return rv;
> >  }
> 
> (scratches head).  Why not do this?
> 
> --- a/fs/proc/base.c~proc-simpler-iterations-for-proc-cmdline-fix
> +++ a/fs/proc/base.c
> @@ -363,11 +363,8 @@ static ssize_t proc_pid_cmdline_read(str
>  	}
>  
>  end:
> -	free_page((unsigned long)page);
> -	mmput(mm);
>  	*pos += buf - buf0;
> -	return buf - buf0;
> -
> +	rv = buf - buf0;
>  out_free_page:
>  	free_page((unsigned long)page);
>  out_mmput:
> 
> (and maybe rv should be ssize_t)

It should as cmdline area can be set to arbitrary values.

I hate ssize_t and it's bloat.

	$ ./scripts/bloat-o-meter ../vmlinux-000 ../obj/vmlinux
	add/remove: 0/0 grow/shrink: 1/0 up/down: 11/0 (11)
	Function                                     old     new   delta
	proc_pid_cmdline_read                        867     878     +11