linux-kernel - Re: [PATCH 1/2] mm/filemap: fix find_lock

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Message-ID: <20210422010630.GK3596236@casper.infradead.org>
Date:   Thu, 22 Apr 2021 02:06:30 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        William Kucharski <william.kucharski@...cle.com>,
        Christoph Hellwig <hch@....de>, Jan Kara <jack@...e.cz>,
        Dave Chinner <dchinner@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/2] mm/filemap: fix find_lock_entries hang on 32-bit THP

On Wed, Apr 21, 2021 at 05:37:33PM -0700, Hugh Dickins wrote:
> -		if (!xa_is_value(page) && PageTransHuge(page))
> -			xas_set(&xas, page->index + thp_nr_pages(page));
> +		if (!xa_is_value(page) && PageTransHuge(page)) {
> +			unsigned int nr_pages = thp_nr_pages(page);
> +
> +			/* Final THP may cross MAX_LFS_FILESIZE on 32-bit */
> +			xas_set(&xas, page->index + nr_pages);
> +			if (xas.xa_index < nr_pages)
> +				break;
> +		}

Aargh.  We really need to get the multi-index support in; this works
perfectly when the xas_set() hack isn't needed any more.