Re: [PATCH 1/5] mmap: don't assume f_op->mmap() doesn't change vma->vm_file

Hugh Dickins
2009-04-14T20:01:34Z

On Tue, 14 Apr 2009, Tejun Heo wrote:

> mmap_region() assumes that vma->vm_file isn't changed by f_op->mmap()
> and continues to use cache file after f_op->mmap() returns.

It does use "file" again in the unmap_and_free_vma error path
(isn't that reasonable? if the ->mmap failed, it shouldn't have
mucked with vma; and even if it has, then we'd better not change
the current behaviour of which to fput), but I don't see where else.

Further down, covering both vma->vm_file previously set and previously
unset cases, there is a "file = vma->vm_file;" before file is used.
So I think this patch is not necessary - if it is necessary, it's
already a bug, because already we switch from /dev/zero to a
shmem file there.

Hugh

> Don't assume that. This will be used by FUSE to redirect mmap to
> shmem_file.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Nick Piggin <npiggin@suse.de>
> ---
> mm/mmap.c | 1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 4a38411..46a7ae5 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1194,6 +1194,7 @@ munmap_back:
> vma->vm_file = file;
> get_file(file);
> error = file->f_op->mmap(file, vma);
> + file = vma->vm_file;
> if (error)
> goto unmap_and_free_vma;
> if (vm_flags & VM_EXECUTABLE)
> --
> 1.6.0.2