mm: mmap_region: kill correct_wcount/inode, use allow_write_access() (e8686772) · Commits · 戴 / test

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>

mm/mmap.c

+5 −9

Original line number	Diff line number	Diff line
		@@ -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 @@ 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);
		@@ -1593,11 +1590,10 @@ 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);

		@@ -1616,8 +1612,8 @@ 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);

Admin message