linux-kernel - Re: [PATCH v3 07/12] mm/debug_vm_pgtable: Use struct pgtable_debug

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Date:   Fri, 23 Jul 2021 08:09:32 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Gavin Shan <gshan@...hat.com>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, catalin.marinas@....com,
        will@...nel.org, akpm@...ux-foundation.org, chuhu@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH v3 07/12] mm/debug_vm_pgtable: Use struct
 pgtable_debug_args in PTE modifying tests



On 7/22/21 12:07 PM, Gavin Shan wrote:
> 
>>>         pgdp = pgd_offset(mm, vaddr);
>>>       p4dp = p4d_alloc(mm, pgdp, vaddr);
>>> @@ -1272,11 +1275,11 @@ static int __init debug_vm_pgtable(void)
>>>        * Page table modifying tests. They need to hold
>>>        * proper page table lock.
>>>        */
>>> -
>>> -    ptep = pte_offset_map_lock(mm, pmdp, vaddr, &ptl);
>>> -    pte_clear_tests(mm, ptep, pte_aligned, vaddr, prot);
>>> -    pte_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
>>> -    pte_unmap_unlock(ptep, ptl);
>>> +    ptl = pte_lockptr(args.mm, args.pmdp);
>>> +    spin_lock(ptl);
>>> +    pte_clear_tests(&args);
>>> +    pte_advanced_tests(&args);
>>> +    spin_unlock(ptl);
>>
>> Why pte_offset_map_lock()/pte_unmap_unlock() has been dropped and
>> spin_lock()/spin_unlock() sequence has been added ? Please dont
>> change the tests in these patches.
>>
> 
> The semantics of pte_offset_map_lock() is to grab and take the lock
> and return the PTE entry, which is mapped if needed. We already had
> the PTE entry tracked by args->ptep in init_args(). So some of the
> operations covered by pte_offset_map_lock() isn't needed any more

To keep the patch on purpose, please avoid this change here. But if
required, you could send a follow up patch later.