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mm: mmap: merge vma after call_mmap() if possible 

The vm_flags may be changed after call_mmap() because drivers may set some
flags for their own purpose.  As a result, we failed to merge the adjacent
vma due to the different vm_flags as userspace can't pass in the same one.
Try to merge vma after call_mmap() to fix this issue.

Signed-off-by: Hongxiang Lou <louhongxiang@huawei.com>
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1594954065-23733-1-git-send-email-linmiaohe@huawei.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Miaohe Lin 2020-08-06 23:23:34 -07:00 committed by Linus Torvalds
parent eee07935bb
commit d70cec8983
1 changed files with 21 additions and 1 deletions
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22
mm/mmap.c
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@ -1690,7 +1690,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
struct list_head *uf)
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma, *prev;
struct vm_area_struct *vma, *prev, *merge;
int error;
struct rb_node **rb_link, *rb_parent;
unsigned long charged = 0;
@ -1774,6 +1774,25 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
if (error)
goto unmap_and_free_vma;
/* If vm_flags changed after call_mmap(), we should try merge vma again
* as we may succeed this time.
*/
if (unlikely(vm_flags != vma->vm_flags && prev)) {
merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags,
NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX);
if (merge) {
fput(file);
vm_area_free(vma);
vma = merge;
/* Update vm_flags and possible addr to pick up the change. We don't
* warn here if addr changed as the vma is not linked by vma_link().
*/
addr = vma->vm_start;
vm_flags = vma->vm_flags;
goto unmap_writable;
}
}
/* Can addr have changed??
*
* Answer: Yes, several device drivers can do it in their
@ -1796,6 +1815,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
vma_link(mm, vma, prev, rb_link, rb_parent);
/* Once vma denies write, undo our temporary denial count */
if (file) {
unmap_writable:
if (vm_flags & VM_SHARED)
mapping_unmap_writable(file->f_mapping);
if (vm_flags & VM_DENYWRITE)