linux-kernel - Re: [PATCH 05/31] mm/filemap: allow pte_offset_map

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Date:   Mon, 22 May 2023 19:23:41 +0800
From:   Qi Zheng <qi.zheng@...ux.dev>
To:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Yang Shi <shy828301@...il.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Peter Xu <peterx@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Alistair Popple <apopple@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Steven Price <steven.price@....com>,
        SeongJae Park <sj@...nel.org>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Zack Rusin <zackr@...are.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Minchan Kim <minchan@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Song Liu <song@...nel.org>,
        Thomas Hellstrom <thomas.hellstrom@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 05/31] mm/filemap: allow pte_offset_map_lock() to fail



On 2023/5/22 12:54, Hugh Dickins wrote:
> filemap_map_pages() allow pte_offset_map_lock() to fail; and remove the
> pmd_devmap_trans_unstable() check from filemap_map_pmd(), which can safely
> return to filemap_map_pages() and let pte_offset_map_lock() discover that.
> 
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> ---
>   mm/filemap.c | 12 +++++-------
>   1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 28b42ee848a4..9e129ad43e0d 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3408,13 +3408,6 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct folio *folio,
>   	if (pmd_none(*vmf->pmd))
>   		pmd_install(mm, vmf->pmd, &vmf->prealloc_pte);
>   
> -	/* See comment in handle_pte_fault() */
> -	if (pmd_devmap_trans_unstable(vmf->pmd)) {
> -		folio_unlock(folio);
> -		folio_put(folio);
> -		return true;
> -	}
> -
>   	return false;
>   }
>   
> @@ -3501,6 +3494,11 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
>   
>   	addr = vma->vm_start + ((start_pgoff - vma->vm_pgoff) << PAGE_SHIFT);
>   	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl);
> +	if (!vmf->pte) {
> +		folio_unlock(folio);
> +		folio_put(folio);

Missing:
		ret = VM_FAULT_NOPAGE;
?

> +		goto out;
> +	}
>   	do {
>   again:
>   		page = folio_file_page(folio, xas.xa_index);

-- 
Thanks,
Qi