linux-kernel - Re: mm: BUG in do_huge_pmd_wp

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Date:	Mon, 07 Apr 2014 15:40:46 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hugh Dickins <hughd@...gle.com>
CC:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Mel Gorman <mgorman@...e.de>,
	Dave Jones <davej@...hat.com>, linux-mm <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: mm: BUG in do_huge_pmd_wp_page

It also breaks fairly quickly under testing because:

On 04/07/2014 10:48 AM, Kirill A. Shutemov wrote:
> +	if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
> +		spin_lock(ptl);

^ We go into atomic

> +		if (unlikely(!pmd_same(*pmd, orig_pmd)))
> +			goto out_race;
> +	}
> +
>  	if (!page)
>  		clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
>  	else
>  		copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);

copy_user_huge_page() doesn't like running in atomic state,
and asserts might_sleep().


Thanks,
Sasha
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