linux-kernel - Re: [PATCH v9 14/24] mm: Introduce __maybe

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Date:   Wed, 4 Apr 2018 17:56:46 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        akpm@...ux-foundation.org, kirill@...temov.name,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>,
        benh@...nel.crashing.org, mpe@...erman.id.au, paulus@...ba.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        kemi.wang@...el.com, sergey.senozhatsky.work@...il.com,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v9 14/24] mm: Introduce __maybe_mkwrite()

On 03/04/2018 01:12, David Rientjes wrote:
> On Tue, 13 Mar 2018, Laurent Dufour wrote:
> 
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index dfa81a638b7c..a84ddc218bbd 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -684,13 +684,18 @@ void free_compound_page(struct page *page);
>>   * pte_mkwrite.  But get_user_pages can cause write faults for mappings
>>   * that do not have writing enabled, when used by access_process_vm.
>>   */
>> -static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
>> +static inline pte_t __maybe_mkwrite(pte_t pte, unsigned long vma_flags)
>>  {
>> -	if (likely(vma->vm_flags & VM_WRITE))
>> +	if (likely(vma_flags & VM_WRITE))
>>  		pte = pte_mkwrite(pte);
>>  	return pte;
>>  }
>>  
>> +static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
>> +{
>> +	return __maybe_mkwrite(pte, vma->vm_flags);
>> +}
>> +
>>  int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
>>  		struct page *page);
>>  int finish_fault(struct vm_fault *vmf);
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 0a0a483d9a65..af0338fbc34d 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -2472,7 +2472,7 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
>>  
>>  	flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
>>  	entry = pte_mkyoung(vmf->orig_pte);
>> -	entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>> +	entry = __maybe_mkwrite(pte_mkdirty(entry), vmf->vma_flags);
>>  	if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
>>  		update_mmu_cache(vma, vmf->address, vmf->pte);
>>  	pte_unmap_unlock(vmf->pte, vmf->ptl);
>> @@ -2549,8 +2549,8 @@ static int wp_page_copy(struct vm_fault *vmf)
>>  			inc_mm_counter_fast(mm, MM_ANONPAGES);
>>  		}
>>  		flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
>> -		entry = mk_pte(new_page, vma->vm_page_prot);
>> -		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>> +		entry = mk_pte(new_page, vmf->vma_page_prot);
>> +		entry = __maybe_mkwrite(pte_mkdirty(entry), vmf->vma_flags);
>>  		/*
>>  		 * Clear the pte entry and flush it first, before updating the
>>  		 * pte with the new entry. This will avoid a race condition
> 
> Don't you also need to do this in do_swap_page()?

Indeed I'll drop this patch as all the changes are now done in the patch 11
"mm: Cache some VMA fields in the vm_fault structure" where, as you suggested,
maybe_mkwrite() is now getting passed the vm_flags value directly.

> diff --git a/mm/memory.c b/mm/memory.c
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3067,9 +3067,9 @@ int do_swap_page(struct vm_fault *vmf)
> 
>  	inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
>  	dec_mm_counter_fast(vma->vm_mm, MM_SWAPENTS);
> -	pte = mk_pte(page, vma->vm_page_prot);
> +	pte = mk_pte(page, vmf->vma_page_prot);
>  	if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page, NULL)) {
> -		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
> +		pte = __maybe_mkwrite(pte_mkdirty(pte), vmf->vma_flags);
>  		vmf->flags &= ~FAULT_FLAG_WRITE;
>  		ret |= VM_FAULT_WRITE;
>  		exclusive = RMAP_EXCLUSIVE;
>