linux-kernel - Re: [PATCH 17/31] mm/various: give up if pte_offset_map[

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Date:   Mon, 22 May 2023 20:37:31 +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 17/31] mm/various: give up if pte_offset_map[_lock]()
 fails



On 2023/5/22 20:24, Qi Zheng wrote:
> 
> 
> 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@...gle.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?

Oh, I see that you handle it in the PATCH[22/31].

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

-- 
Thanks,
Qi