linux-kernel - Re: [PATCH 1/2] sparc: Fix handling of page table constructor failure

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Message-ID: <5b574e0d-107a-3ebc-d631-b59e88de7174@redhat.com>
Date:   Wed, 25 Nov 2020 14:24:29 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     akpm@...ux-foundation.org, davem@...emloft.net, rppt@...nel.org,
        sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/2] sparc: Fix handling of page table constructor failure

On 25.11.20 13:10, Matthew Wilcox wrote:
> On Wed, Nov 25, 2020 at 09:43:15AM +0100, David Hildenbrand wrote:
>> On 25.11.20 04:46, Matthew Wilcox (Oracle) wrote:
>>> The page has just been allocated, so its refcount is 1.  free_unref_page()
>>> is for use on pages which have a zero refcount.  Use __free_page()
>>> like the other implementations of pte_alloc_one().
>>>
>>> Fixes: 1ae9ae5f7df7 ("sparc: handle pgtable_page_ctor() fail")
>>> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
>>> ---
>>>  arch/sparc/mm/init_64.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
>>> index 96edf64d4fb3..182bb7bdaa0a 100644
>>> --- a/arch/sparc/mm/init_64.c
>>> +++ b/arch/sparc/mm/init_64.c
>>> @@ -2894,7 +2894,7 @@ pgtable_t pte_alloc_one(struct mm_struct *mm)
>>>  	if (!page)
>>>  		return NULL;
>>>  	if (!pgtable_pte_page_ctor(page)) {
>>> -		free_unref_page(page);
>>> +		__free_page(page);
>>>  		return NULL;
>>>  	}
>>>  	return (pte_t *) page_address(page);
>>>
>>
>> I wonder if reusing __pte_alloc_one() - e.g., internally - would be even
>> cleaner.
> 
> It's really awkward to do because pgtable_t is defined differently.
> The clean thing to do would be:
> 
> --- arch/sparc/include/asm/page_64.h
> -typedef pte_t *pgtable_t;
> +typedef struct page *pgtable_t;
> 
> and then do all the other changes that would require.
> 
> But that feels like a lot more work than appropriate to fix this
> unlikely bug.

Yeah, cleanups would have to come on top of the fix of course. But I can
understand that you have plenty of better things to do :) ... maybe
sparc people want to work on that at one point.

-- 
Thanks,

David / dhildenb