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Message-ID: <8f6057b5-362b-a0f6-2f2f-579debe48fce@linux.dev>
Date:   Mon, 22 May 2023 19:23:41 +0800
MIME-Version: 1.0
Subject: Re: [PATCH 05/31] mm/filemap: allow pte_offset_map_lock() to fail
Content-Language: en-US
To:     Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        David Hildenbrand <david@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Qi Zheng <zhengqi.arch@bytedance.com>,
        Yang Shi <shy828301@gmail.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Peter Xu <peterx@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>,
        Alistair Popple <apopple@nvidia.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Steven Price <steven.price@arm.com>,
        SeongJae Park <sj@kernel.org>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Zack Rusin <zackr@vmware.com>, Jason Gunthorpe <jgg@ziepe.ca>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Minchan Kim <minchan@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Song Liu <song@kernel.org>,
        Thomas Hellstrom <thomas.hellstrom@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com>
 <3e6d4f8-9f4d-fa7e-304e-1494dddd45b@google.com>
From:   Qi Zheng <qi.zheng@linux.dev>
In-Reply-To: <3e6d4f8-9f4d-fa7e-304e-1494dddd45b@google.com>
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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@google.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