Re: [PATCH -v5 1/2] Massive code cleanup of sys_msync()

[Miklos Szeredi <miklos@szeredi.hu>]

> Substantial code cleanup of the sys_msync() function:
> 
> 1) using the PAGE_ALIGN() macro instead of "manual" alignment;
> 2) improved readability of the loop traversing the process memory regions.
> 
> Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>
> ---
>  mm/msync.c |   74 +++++++++++++++++++++++++++++------------------------------
>  1 files changed, 36 insertions(+), 38 deletions(-)
> 
> diff --git a/mm/msync.c b/mm/msync.c
> index 144a757..44997bf 100644
> --- a/mm/msync.c
> +++ b/mm/msync.c
> @@ -1,24 +1,22 @@
>  /*
> - *	linux/mm/msync.c
> + * The msync() system call.
>   *
> - * Copyright (C) 1994-1999  Linus Torvalds
> + * Copyright (C) 1994-1999 Linus Torvalds
> + * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@gmail.com>
>   */
>  
> -/*
> - * The msync() system call.
> - */
> +#include <linux/file.h>
>  #include <linux/fs.h>
>  #include <linux/mm.h>
>  #include <linux/mman.h>
> -#include <linux/file.h>
> -#include <linux/syscalls.h>
>  #include <linux/sched.h>
> +#include <linux/syscalls.h>
>  
>  /*
>   * MS_SYNC syncs the entire file - including mappings.
>   *
>   * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
> - * Nor does it marks the relevant pages dirty (it used to up to 2.6.17).
> + * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
>   * Now it doesn't do anything, since dirty pages are properly tracked.
>   *
>   * The application may now run fsync() to
> @@ -33,8 +31,7 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
>  	unsigned long end;
>  	struct mm_struct *mm = current->mm;
>  	struct vm_area_struct *vma;
> -	int unmapped_error = 0;
> -	int error = -EINVAL;
> +	int error = -EINVAL, unmapped_error = 0;

I prefer multi-line variable declarations, especially for ones with an
initializer.

>  
>  	if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
>  		goto out;
> @@ -42,62 +39,63 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
>  		goto out;
>  	if ((flags & MS_ASYNC) && (flags & MS_SYNC))
>  		goto out;
> -	error = -ENOMEM;
> -	len = (len + ~PAGE_MASK) & PAGE_MASK;
> +
> +	len = PAGE_ALIGN(len);
>  	end = start + len;
> -	if (end < start)
> +	if (end < start) {
> +		error = -ENOMEM;

The usual style is to have the error assignment outside the
conditional.  That way is shorter, clearer, as well as possibly
generating better code.

>  		goto out;
> +	}
> +
>  	error = 0;
> +

Unnecessary empty line here, these two statements actually belong
together.

>  	if (end == start)
>  		goto out;
> +
>  	/*
>  	 * If the interval [start,end) covers some unmapped address ranges,
>  	 * just ignore them, but return -ENOMEM at the end.
>  	 */
>  	down_read(&mm->mmap_sem);
>  	vma = find_vma(mm, start);
> -	for (;;) {
> +	do {
>  		struct file *file;
>  
> -		/* Still start < end. */
> -		error = -ENOMEM;
> -		if (!vma)
> -			goto out_unlock;
> -		/* Here start < vma->vm_end. */
> +		if (!vma) {
> +			error = -ENOMEM;
> +			break;
> +		}

Again, error asignment should be outside the conditional.  This of
course means, you'll have to set the error back to zero at the end of
the loop, but that's fine.

>  		if (start < vma->vm_start) {
>  			start = vma->vm_start;
> -			if (start >= end)
> -				goto out_unlock;
> +			if (start >= end) {
> +				error = -ENOMEM;
> +				break;
> +			}

Ditto.

>  			unmapped_error = -ENOMEM;
>  		}
> -		/* Here vma->vm_start <= start < vma->vm_end. */
> -		if ((flags & MS_INVALIDATE) &&
> -				(vma->vm_flags & VM_LOCKED)) {
> +		if ((flags & MS_INVALIDATE) && (vma->vm_flags & VM_LOCKED)) {
>  			error = -EBUSY;

Ditto2.

> -			goto out_unlock;
> +			break;
>  		}
> -		file = vma->vm_file;
>  		start = vma->vm_end;
> -		if ((flags & MS_SYNC) && file &&
> -				(vma->vm_flags & VM_SHARED)) {
> +
> +		file = vma->vm_file;
> +		if (file && (vma->vm_flags & VM_SHARED) && (flags & MS_SYNC)) {
>  			get_file(file);
>  			up_read(&mm->mmap_sem);
>  			error = do_fsync(file, 0);
>  			fput(file);
> -			if (error || start >= end)
> +			if (error)

This simplifies, but also does unnecessary down/find_vma/up.

>  				goto out;
>  			down_read(&mm->mmap_sem);
>  			vma = find_vma(mm, start);
> -		} else {
> -			if (start >= end) {
> -				error = 0;
> -				goto out_unlock;
> -			}
> -			vma = vma->vm_next;
> +			continue;
>  		}
> -	}
> -out_unlock:
> +
> +		vma = vma->vm_next;
> +	} while (start < end);
>  	up_read(&mm->mmap_sem);
> +
>  out:
> -	return error ? : unmapped_error;
> +	return error ? error : unmapped_error;
>  }

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