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

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Message-ID: <Pine.LNX.4.64.0904142047410.16616@blonde.anvils>
Date:	Tue, 14 Apr 2009 20:59:24 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Tejun Heo <tj@...nel.org>
cc:	linux-kernel@...r.kernel.org, fuse-devel@...ts.sourceforge.net,
	miklos@...redi.hu, akpm@...ux-foundation.org, npiggin@...e.de
Subject: Re: [PATCH 1/5] mmap: don't assume f_op->mmap() doesn't change
 vma->vm_file

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@...nel.org>
> Cc: Nick Piggin <npiggin@...e.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
--
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