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Date: Fri, 23 Mar 2012 15:45:02 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Jan Kara <jack@suse.cz>
Cc: LKML <linux-kernel@vger.kernel.org>, linux-fsdevel@vger.kernel.org,
        Al Viro <viro@ZenIV.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>, dchinner@redhat.com,
        sandeen@redhat.com, Kamal Mostafa <kamal@canonical.com>
Subject: Re: [PATCH 01/19] mm: Make default vm_ops provide ->page_mkwrite
 handler
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On Mon,  5 Mar 2012 17:00:59 +0100
Jan Kara <jack@suse.cz> wrote:

> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1759,8 +1759,28 @@ page_not_uptodate:
>  }
>  EXPORT_SYMBOL(filemap_fault);
>  
> +int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> +	struct page *page = vmf->page;
> +	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
> +	int ret = VM_FAULT_LOCKED;
> +
> +	file_update_time(vma->vm_file);
> +	lock_page(page);
> +	if ((page->mapping != inode->i_mapping) ||
> +	    (page_offset(page) > i_size_read(inode))) {

Would benefit from a comment explaining how the page can come to be
outside i_size, and why we fail in that case.

I don't think i_mutex is held here, so this test is rather meaningless
and racy anyway?

> +		unlock_page(page);
> +		ret = VM_FAULT_NOPAGE;
> +		goto out;
> +	}
> +out:
> +	return ret;
> +}
> +EXPORT_SYMBOL(filemap_page_mkwrite);