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mm/mmap.c: replace find_vma_prepare() with clearer find_vma_links()
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People get confused by find_vma_prepare(), because it doesn't care about
what it returns in its output args, when its callers won't be interested.

Clarify by passing in end-of-range address too, and returning failure if
any existing vma overlaps the new range: instead of returning an ambiguous
vma which most callers then must check.  find_vma_links() is a clearer
name.

This does revert 2.6.27's dfe195f ("mm: fix uninitialized variables
for find_vma_prepare callers"), but it looks like gcc 4.3.0 was one of
those releases too eager to shout about uninitialized variables: only
copy_vma() warns with 4.5.1 and 4.7.1, which a BUG on error silences.

[hughd@google.com: fix warning, remove BUG()]
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Benny Halevy <bhalevy@tonian.com>
Acked-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Hugh Dickins authored and Linus Torvalds committed Oct 9, 2012
1 parent d741c9c commit 6597d78
Showing 1 changed file with 21 additions and 24 deletions.
45 changes: 21 additions & 24 deletions mm/mmap.c
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Original file line number Diff line number Diff line change
Expand Up @@ -353,17 +353,14 @@ void validate_mm(struct mm_struct *mm)
#define validate_mm(mm) do { } while (0)
#endif

static struct vm_area_struct *
find_vma_prepare(struct mm_struct *mm, unsigned long addr,
struct vm_area_struct **pprev, struct rb_node ***rb_link,
struct rb_node ** rb_parent)
static int find_vma_links(struct mm_struct *mm, unsigned long addr,
unsigned long end, struct vm_area_struct **pprev,
struct rb_node ***rb_link, struct rb_node **rb_parent)
{
struct vm_area_struct * vma;
struct rb_node ** __rb_link, * __rb_parent, * rb_prev;
struct rb_node **__rb_link, *__rb_parent, *rb_prev;

__rb_link = &mm->mm_rb.rb_node;
rb_prev = __rb_parent = NULL;
vma = NULL;

while (*__rb_link) {
struct vm_area_struct *vma_tmp;
Expand All @@ -372,9 +369,9 @@ find_vma_prepare(struct mm_struct *mm, unsigned long addr,
vma_tmp = rb_entry(__rb_parent, struct vm_area_struct, vm_rb);

if (vma_tmp->vm_end > addr) {
vma = vma_tmp;
if (vma_tmp->vm_start <= addr)
break;
/* Fail if an existing vma overlaps the area */
if (vma_tmp->vm_start < end)
return -ENOMEM;
__rb_link = &__rb_parent->rb_left;
} else {
rb_prev = __rb_parent;
Expand All @@ -387,7 +384,7 @@ find_vma_prepare(struct mm_struct *mm, unsigned long addr,
*pprev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);
*rb_link = __rb_link;
*rb_parent = __rb_parent;
return vma;
return 0;
}

void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
Expand Down Expand Up @@ -456,11 +453,12 @@ static void vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
*/
static void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
{
struct vm_area_struct *__vma, *prev;
struct vm_area_struct *prev;
struct rb_node **rb_link, *rb_parent;

__vma = find_vma_prepare(mm, vma->vm_start,&prev, &rb_link, &rb_parent);
BUG_ON(__vma && __vma->vm_start < vma->vm_end);
if (find_vma_links(mm, vma->vm_start, vma->vm_end,
&prev, &rb_link, &rb_parent))
BUG();
__vma_link(mm, vma, prev, rb_link, rb_parent);
mm->map_count++;
}
Expand Down Expand Up @@ -1221,8 +1219,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
/* Clear old maps */
error = -ENOMEM;
munmap_back:
vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
if (vma && vma->vm_start < addr + len) {
if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) {
if (do_munmap(mm, addr, len))
return -ENOMEM;
goto munmap_back;
Expand Down Expand Up @@ -2183,8 +2180,7 @@ static unsigned long do_brk(unsigned long addr, unsigned long len)
* Clear old maps. this also does some error checking for us
*/
munmap_back:
vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
if (vma && vma->vm_start < addr + len) {
if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) {
if (do_munmap(mm, addr, len))
return -ENOMEM;
goto munmap_back;
Expand Down Expand Up @@ -2298,10 +2294,10 @@ void exit_mmap(struct mm_struct *mm)
* and into the inode's i_mmap tree. If vm_file is non-NULL
* then i_mmap_mutex is taken here.
*/
int insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
{
struct vm_area_struct * __vma, * prev;
struct rb_node ** rb_link, * rb_parent;
struct vm_area_struct *prev;
struct rb_node **rb_link, *rb_parent;

/*
* The vm_pgoff of a purely anonymous vma should be irrelevant
Expand All @@ -2319,8 +2315,8 @@ int insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
BUG_ON(vma->anon_vma);
vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
}
__vma = find_vma_prepare(mm,vma->vm_start,&prev,&rb_link,&rb_parent);
if (__vma && __vma->vm_start < vma->vm_end)
if (find_vma_links(mm, vma->vm_start, vma->vm_end,
&prev, &rb_link, &rb_parent))
return -ENOMEM;
if ((vma->vm_flags & VM_ACCOUNT) &&
security_vm_enough_memory_mm(mm, vma_pages(vma)))
Expand Down Expand Up @@ -2354,7 +2350,8 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
faulted_in_anon_vma = false;
}

find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent))
return NULL; /* should never get here */
new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
if (new_vma) {
Expand Down

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