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mm: mmap_region: kill correct_wcount/inode, use allow_write_access()
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correct_wcount and inode in mmap_region() just complicate the code.  This
boolean was needed previously, when deny_write_access() was called before
vma_merge(), now we can simply check VM_DENYWRITE and do
allow_write_access() if it is set.

allow_write_access() checks file != NULL, so this is safe even if it was
possible to use VM_DENYWRITE && !file.  Just we need to ensure we use the
same file which was deny_write_access()'ed, so the patch also moves "file
= vma->vm_file" down after allow_write_access().

Signed-off-by: Oleg Nesterov <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Colin Cross <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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oleg-nesterov authored and torvalds committed Sep 11, 2013
1 parent 077bf22 commit e868677
Showing 1 changed file with 5 additions and 9 deletions.
14 changes: 5 additions & 9 deletions mm/mmap.c
Original file line number Diff line number Diff line change
@@ -1479,11 +1479,9 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma, *prev;
int correct_wcount = 0;
int error;
struct rb_node **rb_link, *rb_parent;
unsigned long charged = 0;
struct inode *inode = file ? file_inode(file) : NULL;

/* Check against address space limit. */
if (!may_expand_vm(mm, len >> PAGE_SHIFT)) {
@@ -1552,7 +1550,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
error = deny_write_access(file);
if (error)
goto free_vma;
correct_wcount = 1;
}
vma->vm_file = get_file(file);
error = file->f_op->mmap(file, vma);
@@ -1593,11 +1590,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
}

vma_link(mm, vma, prev, rb_link, rb_parent);
file = vma->vm_file;

/* Once vma denies write, undo our temporary denial count */
if (correct_wcount)
atomic_inc(&inode->i_writecount);
if (vm_flags & VM_DENYWRITE)
allow_write_access(file);
file = vma->vm_file;
out:
perf_event_mmap(vma);

@@ -1616,8 +1612,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
return addr;

unmap_and_free_vma:
if (correct_wcount)
atomic_inc(&inode->i_writecount);
if (vm_flags & VM_DENYWRITE)
allow_write_access(file);
vma->vm_file = NULL;
fput(file);

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