[PATCH 4/6] mremap vma_relink_file

From: Hugh Dickins (hugh_at_veritas.com)
Date: 03/31/04

  • Next message: Robert Olsson: "Re: route cache DoS testing and softirqs" 
    Date:	Tue, 30 Mar 2004 23:47:02 +0100 (BST)
To: Andrew Morton <akpm@osdl.org>

    Subtle point from Rajesh Venkatasubramanian: when mremap's move_vma
    fails and so rewinds, before moving the file-based ptes back, we must
    move new_vma before old vma in the i_mmap or i_mmap_shared list,
    so that when racing against vmtruncate we cannot propagate pages
    to be truncated back from new_vma into the just cleaned old_vma.

    --- mremap3/include/linux/mm.h 2004-03-30 21:24:48.666410384 +0100
    +++ mremap4/include/linux/mm.h 2004-03-30 21:25:00.131667400 +0100
    @@ -540,6 +540,7 @@ extern void __vma_link_rb(struct mm_stru
             struct rb_node **, struct rb_node *);
     extern struct vm_area_struct *copy_vma(struct vm_area_struct *,
             unsigned long addr, unsigned long len, unsigned long pgoff);
    +extern void vma_relink_file(struct vm_area_struct *, struct vm_area_struct *);
     extern void exit_mmap(struct mm_struct *);
     
     extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
    --- mremap3/mm/mmap.c 2004-03-30 21:24:48.668410080 +0100
    +++ mremap4/mm/mmap.c 2004-03-30 21:25:00.133667096 +0100
    @@ -1517,3 +1517,24 @@ struct vm_area_struct *copy_vma(struct v
             }
             return new_vma;
     }
    +
    +/*
    + * Position vma after prev in shared file list:
    + * for mremap move error recovery racing against vmtruncate.
    + */
    +void vma_relink_file(struct vm_area_struct *vma, struct vm_area_struct *prev)
    +{
    + struct mm_struct *mm = vma->vm_mm;
    + struct address_space *mapping;
    +
    + if (vma->vm_file) {
    + mapping = vma->vm_file->f_mapping;
    + if (mapping) {
    + down(&mapping->i_shared_sem);
    + spin_lock(&mm->page_table_lock);
    + list_move(&vma->shared, &prev->shared);
    + spin_unlock(&mm->page_table_lock);
    + up(&mapping->i_shared_sem);
    + }
    + }
    +}
    --- mremap3/mm/mremap.c 2004-03-30 21:24:48.671409624 +0100
    +++ mremap4/mm/mremap.c 2004-03-30 21:25:00.136666640 +0100
    @@ -187,7 +187,14 @@ static unsigned long move_vma(struct vm_
                      * On error, move entries back from new area to old,
                      * which will succeed since page tables still there,
                      * and then proceed to unmap new area instead of old.
    + *
    + * Subtle point from Rajesh Venkatasubramanian: before
    + * moving file-based ptes, move new_vma before old vma
    + * in the i_mmap or i_mmap_shared list, so when racing
    + * against vmtruncate we cannot propagate pages to be
    + * truncated back from new_vma into just cleaned old.
                      */
    + vma_relink_file(vma, new_vma);
                     move_page_tables(new_vma, old_addr, new_addr, moved_len);
                     vma = new_vma;
                     old_len = new_len;

    -
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