From: Miaohe Lin <linmiaohe@xxxxxxxxxx> Subject: 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. Link: http://lkml.kernel.org/r/1594954065-23733-1-git-send-email-linmiaohe@xxxxxxxxxx Signed-off-by: Hongxiang Lou <louhongxiang@xxxxxxxxxx> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/mmap.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) --- a/mm/mmap.c~mm-mmap-merge-vma-after-call_mmap-if-possible +++ a/mm/mmap.c @@ -1690,7 +1690,7 @@ unsigned long mmap_region(struct file *f 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 *f 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 *f 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) _
