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Message-ID: <f8468e50-9f54-f22d-59a7-3a48369d2f05@linux.dev>
Date:   Mon, 22 May 2023 20:24:45 +0800
MIME-Version: 1.0
Subject: Re: [PATCH 17/31] mm/various: give up if pte_offset_map[_lock]()
 fails
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>
 <c299eba-4e17-c645-1115-ccd1fd9956bd@google.com>
From:   Qi Zheng <qi.zheng@linux.dev>
In-Reply-To: <c299eba-4e17-c645-1115-ccd1fd9956bd@google.com>
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On 2023/5/22 13:10, Hugh Dickins wrote:
> Following the examples of nearby code, various functions can just give
> up if pte_offset_map() or pte_offset_map_lock() fails.  And there's no
> need for a preliminary pmd_trans_unstable() or other such check, since
> such cases are now safely handled inside.
> 
> Signed-off-by: Hugh Dickins <hughd@google.com>
> ---
>   mm/gup.c            | 9 ++++++---
>   mm/ksm.c            | 7 ++++---
>   mm/memcontrol.c     | 8 ++++----
>   mm/memory-failure.c | 8 +++++---
>   mm/migrate.c        | 3 +++
>   mm/swap_state.c     | 3 +++
>   6 files changed, 25 insertions(+), 13 deletions(-)
> 

[...]

> diff --git a/mm/migrate.c b/mm/migrate.c
> index 3ecb7a40075f..308a56f0b156 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -305,6 +305,9 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
>   	swp_entry_t entry;
>   
>   	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
> +	if (!ptep)
> +		return;

Maybe we should return false and let the caller handle the failure.

> +
>   	pte = *ptep;
>   	pte_unmap(ptep);
>   
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index b76a65ac28b3..db2ec85ef332 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -734,6 +734,9 @@ static void swap_ra_info(struct vm_fault *vmf,
>   
>   	/* Copy the PTEs because the page table may be unmapped */
>   	orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
> +	if (!pte)
> +		return;

Ditto?

> +
>   	if (fpfn == pfn + 1) {
>   		lpfn = fpfn;
>   		rpfn = fpfn + win;

-- 
Thanks,
Qi