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Date:   Tue, 4 Jul 2023 00:25:33 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org
Subject: Re: [PATCH 1/4] mm/memory: convert do_page_mkwrite() to use folios
Message-ID: <ZKNY7XOQFYJoHrBS@casper.infradead.org>
References: <20230703055850.227169-1-sidhartha.kumar@oracle.com>
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On Sun, Jul 02, 2023 at 10:58:47PM -0700, Sidhartha Kumar wrote:
> @@ -2947,14 +2947,14 @@ static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
>  	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
>  		return ret;
>  	if (unlikely(!(ret & VM_FAULT_LOCKED))) {
> -		lock_page(page);
> -		if (!page->mapping) {
> -			unlock_page(page);
> +		folio_lock(folio);
> +		if (!folio_mapping(folio)) {

You don't need to call folio_mapping() here.  folio->mapping works
absolutely fine in this circumstance.  In fact, you may have broken a
driver with this change.  I can elaborate more, but I'm not quite in the
mood to do that right now.