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Date: Mon, 14 Jan 2008 14:56:33 +0300
From: "Anton Salikhmetov" <salikhmetov@...il.com>
To: "Miklos Szeredi" <miklos@...redi.hu>
Cc: linux-mm@...ck.org, jakob@...hought.net,
linux-kernel@...r.kernel.org, valdis.kletnieks@...edu,
riel@...hat.com, ksm@...dk, staubach@...hat.com,
jesper.juhl@...il.com, torvalds@...ux-foundation.org,
a.p.zijlstra@...llo.nl, akpm@...ux-foundation.org,
protasnb@...il.com
Subject: Re: [PATCH 1/2] massive code cleanup of sys_msync()
2008/1/14, Miklos Szeredi <miklos@...redi.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.
>
> Thanks for doing this. See comments below.
>
> > Signed-off-by: Anton Salikhmetov <salikhmetov@...il.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@...il.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.
Thanks for your review. I overlooked this problem. I'll redo my cleanup soon.
>
> > - } 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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