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Date:   Thu, 18 Mar 2021 10:29:57 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Oscar Salvador <osalvador@suse.de>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Mike Kravetz <mike.kravetz@oracle.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 4/5] mm: Make alloc_contig_range handle in-use hugetlb
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References: <20210317111251.17808-1-osalvador@suse.de>
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On Thu 18-03-21 09:54:01, Oscar Salvador wrote:
[...]
> @@ -2287,10 +2288,12 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
>  		goto unlock;
>  	} else if (page_count(old_page)) {
>  		/*
> -		 * Someone has grabbed the page, fail for now.
> +		 * Someone has grabbed the page, try to isolate it here.
> +		 * Fail with -EBUSY if not possible.
>  		 */
> -		ret = -EBUSY;
>  		update_and_free_page(h, new_page);
> +		if (!isolate_huge_page(old_page, list)
> +			ret = -EBUSY;
>  		goto unlock;
>  	} else if (!HPageFreed(old_page)) {

I do not think you want to call isolate_huge_page with hugetlb_lock
held. You would need to drop the lock before calling isolate_huge_page.
-- 
Michal Hocko
SUSE Labs