linux-kernel - Re: [PATCH v2 1/5] mm,hugetlb: Change mechanism to detect a COW on private mapping

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Message-ID: <45d66a0c-a5ed-4894-999c-0ed5b732ebb0@redhat.com>
Date: Mon, 23 Jun 2025 16:09:51 +0200
From: David Hildenbrand <david@...hat.com>
To: Oscar Salvador <osalvador@...e.de>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Muchun Song <muchun.song@...ux.dev>, Peter Xu <peterx@...hat.com>,
 Gavin Guo <gavinguo@...lia.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] mm,hugetlb: Change mechanism to detect a COW on
 private mapping


>   
> -	/*
> -	 * hugetlb_wp() requires page locks of pte_page(vmf.orig_pte) and
> -	 * pagecache_folio, so here we need take the former one
> -	 * when folio != pagecache_folio or !pagecache_folio.
> -	 */
> +	/* hugetlb_wp() requires page locks of pte_page(vmf.orig_pte) */
>   	folio = page_folio(pte_page(vmf.orig_pte));
> -	if (folio != pagecache_folio)
> -		if (!folio_trylock(folio)) {
> -			need_wait_lock = 1;
> -			goto out_ptl;
> -		}
> -
> +	folio_lock(folio);
>   	folio_get(folio);

Just realized that this won't work for this patch here, as we are 
holding the PTL.

In patch #2 you do the right thing.

-- 
Cheers,

David / dhildenb