linux-kernel - Re: [PATCH v4 2/2] mm,hwpoison: make get_hwpoison_page call get_any

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Date:   Mon, 17 May 2021 15:13:15 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Oscar Salvador <osalvador@...e.de>
CC:     Naoya Horiguchi <nao.horiguchi@...il.com>,
        Muchun Song <songmuchun@...edance.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Michal Hocko <mhocko@...e.com>,
        Tony Luck <tony.luck@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/2] mm,hwpoison: make get_hwpoison_page call
 get_any_page()

On Mon, May 17, 2021 at 02:59:03PM +0200, Oscar Salvador wrote:
> On Mon, May 17, 2021 at 01:54:01PM +0900, Naoya Horiguchi wrote:
> >  static int __get_hwpoison_page(struct page *page)
> >  {
> >  	struct page *head = compound_head(page);
> > @@ -1098,7 +1091,9 @@ static int __get_hwpoison_page(struct page *page)
> >  
> >  #ifdef CONFIG_HUGETLB_PAGE
> >  	spin_lock(&hugetlb_lock);
> > -	if (PageHuge(head) && (HPageFreed(head) || HPageMigratable(head)))
> > +	if (!PageHuge(head))
> > +		ret = -EBUSY;
> 
> Unless I'm missing something, we will be returning -EBUSY for any non-hugetlb
> page, which is not right.

(sigh, hard to say why I wrote this, really sorry)

> I think what you want is to return -EBUSY in case the page is a hugetlb page
> but we cannot grab a refcount because the page is in a floating state, meaning
> !HPageFreed && !HPageMigratable.
> 
> Right?

Totally right, so the below should what's wanted.

        spin_lock(&hugetlb_lock);
        if (PageHuge(head))
                if (!HPageFreed(head) && !HPageMigratable(head))
                        ret = -EBUSY;
                else
                        ret = get_page_unless_zero(head);
        spin_unlock(&hugetlb_lock);

- Naoya