linux-kernel - Re: [PATCH 8/9] mm/hugetlb: convert hugetlb

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Message-ID: <20230124162346.404985e8@thinkpad>
Date:   Tue, 24 Jan 2023 16:23:46 +0100
From:   Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
To:     Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, songmuchun@...edance.com,
        mike.kravetz@...cle.com, willy@...radead.org, jhubbard@...dia.com,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH 8/9] mm/hugetlb: convert hugetlb_wp() to take in a folio

On Thu, 19 Jan 2023 13:14:45 -0800
Sidhartha Kumar <sidhartha.kumar@...cle.com> wrote:

[...]
>  	page = pte_page(entry);
> -	if (page != pagecache_page)
> +	if (page_folio(page) != pagecache_folio)
>  		if (!trylock_page(page)) {
>  			need_wait_lock = 1;
>  			goto out_ptl;
>  		}
>  
> -	get_page(page);
> +	folio_get(pagecache_folio);
>  

We get a kernel crash on s390 in mprotect testcase from libhugetlbfs
testsuite, starting with next-20230120, bisected to this commit.

We get here with pagecache_folio == NULL, and crash in folio_get().
It doesn´t seem right to replace the get_page() with folio_get()
here, the matching put_page() at out_put_page: also wasn't changed
correspondingly. Also, pagecache_folio == NULL seems to be a valid
case here, on all architectures.

Reverting this folio_get() to get_page() fixes the crash. Not sure
though if I missed something. I think you only want to replace
pagecache_page with pagecache_folio, like in the rest of the commit,
and not page -> pagecache_folio for this get_page().