mm: mmap_region: kill correct_wcount/inode, use allow_write_access()

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 <oleg@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Colin Cross <ccross@android.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Change-Id: I05df8842b7c4b7e3e29b35d914f297ce37af1685
Origin: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=e86867720e617774b560dfbc169b7f3d0d490950
Backported-by: Maciej Wereski <m.wereski@partner.samsung.com>
Signed-off-by: Maciej Wereski <m.wereski@partner.samsung.com>

diff --git a/mm/mmap.c b/mm/mmap.c
index 8f87b14..f97c319 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1474,11 +1474,9 @@ 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)) {
@@ -1551,7 +1549,6 @@ munmap_back:
                        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);
@@ -1594,11 +1591,10 @@ munmap_back:
        }
 
        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);
 
@@ -1617,8 +1613,8 @@ out:
        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);