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Date: Wed, 14 Dec 2016 21:15:19 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Joseph Salisbury <joseph.salisbury@canonical.com>,
        fangwei1@huawei.com, Christoph Hellwig <hch@infradead.org>,
        Dave Chinner <david@fromorbit.com>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [v4.9 Regression] vfs,mm: fix a dead loop in
 truncate_inode_pages_range()
Message-ID: <20161214211519.GP1555@ZenIV.linux.org.uk>
References: <2e0624ac-c0be-de61-d54d-1c1ce39358ae@canonical.com>
 <CA+55aFwVfyQUfQ5-QjosmmKbu95-4EmbgFyTg=SevFbZdcCFbQ@mail.gmail.com>
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On Wed, Dec 14, 2016 at 12:27:41PM -0800, Linus Torvalds wrote:

> diff --git a/mm/filemap.c b/mm/filemap.c
> index 69568388c699..b06517b7f97f 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1637,7 +1637,7 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
>  	int error = 0;
>  
>  	if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
> -		return -EINVAL;
> +		return 0;
>  	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);

BTW, shouldn't we truncate to *ppos - inode->i_sb->s_maxbytes here as well?