linux-kernel - Re: [PATCH v14 01/12] splice: Fix O_DIRECT file read splice to avoid reversion of ITER

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Date:   Mon, 13 Feb 2023 00:22:19 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Matthew Wilcox <willy@...radead.org>, Jens Axboe <axboe@...nel.dk>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hillf Danton <hdanton@...a.com>, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org,
        syzbot+a440341a59e3b7142895@...kaller.appspotmail.com,
        Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH v14 01/12] splice: Fix O_DIRECT file read splice to avoid
 reversion of ITER_PIPE

> +	if (!bv)
> +		return -ENOMEM;
> +
> +	pages = (void *)(bv + npages);

I think this cast should be to struct page **… not void *.

> +	npages = alloc_pages_bulk_array(GFP_USER, npages, pages);
> +	if (!npages) {
> +		kfree(bv);
> +		return -ENOMEM;
> +	}

> +	reclaim = npages * PAGE_SIZE;
> +	remain = 0;
> +	if (ret > 0) {
> +		reclaim -= ret;
> +		remain = ret;

...

> +	/* Free any pages that didn't get touched at all. */
> +	reclaim /= PAGE_SIZE;

Any reason not to keep reclaim in PAGE_SIZE units to start with?