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SubjectRe: [PATCH 1/2] massive code cleanup of sys_msync()
From
Date
> 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.

Thanks for doing this. See comments below.

> Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>
> ---
> mm/msync.c | 78 +++++++++++++++++++++++++++---------------------------------
> 1 files changed, 35 insertions(+), 43 deletions(-)
>
> diff --git a/mm/msync.c b/mm/msync.c
> index 144a757..ff654c9 100644
> --- a/mm/msync.c
> +++ b/mm/msync.c
> @@ -1,24 +1,25 @@
> /*
> * linux/mm/msync.c
> *
> + * The msync() system call.
> * Copyright (C) 1994-1999 Linus Torvalds
> + *
> + * Substantial code cleanup.
> + * 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
> @@ -33,71 +34,62 @@ 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 = 0, unmapped_error = 0;
>
> if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
> - goto out;
> + return -EINVAL;
> if (start & ~PAGE_MASK)
> - goto out;
> + return -EINVAL;
> if ((flags & MS_ASYNC) && (flags & MS_SYNC))
> - goto out;
> - error = -ENOMEM;
> - len = (len + ~PAGE_MASK) & PAGE_MASK;
> + return -EINVAL;
> +
> + len = PAGE_ALIGN(len);
> end = start + len;
> if (end < start)
> - goto out;
> - error = 0;
> + return -ENOMEM;
> if (end == start)
> - goto out;
> + return 0;
> +
> /*
> * 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;
> + }
> if (start < vma->vm_start) {
> start = vma->vm_start;
> - if (start >= end)
> - goto out_unlock;
> + if (start >= end) {
> + error = -ENOMEM;
> + break;
> + }
> 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;
> - goto out_unlock;
> + break;
> }
> file = vma->vm_file;
> - start = vma->vm_end;
> - if ((flags & MS_SYNC) && file &&
> - (vma->vm_flags & VM_SHARED)) {
> + if ((flags & MS_SYNC) && file && (vma->vm_flags & VM_SHARED)) {
> get_file(file);
> up_read(&mm->mmap_sem);
> error = do_fsync(file, 0);
> fput(file);
> - if (error || start >= end)
> - goto out;
> + if (error)
> + return error;
> down_read(&mm->mmap_sem);
> - vma = find_vma(mm, start);

Where did this line go? It's needed because after releasing and
reacquiring the mmap sem, the old vma may have gone away.

I suggest, that when doing such a massive cleanup, that you split it
up even further into easily understandable pieces, so such bugs cannot
creep in.

> - } else {
> - if (start >= end) {
> - error = 0;
> - goto out_unlock;
> - }
> - vma = vma->vm_next;
> }
> - }
> -out_unlock:
> +
> + start = vma->vm_end;
> + vma = vma->vm_next;
> + } while (start < end);
> up_read(&mm->mmap_sem);
> -out:
> +
> return error ? : unmapped_error;
> }
> --
> 1.4.4.4

Miklos


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