[v2,1/3] mm: change huge_ptep_clear_flush() to return the original pte

Commit Message

Baolin Wang May 8, 2022, 9:36 a.m. UTC

It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
table when unmapping or migrating a hugetlb page, and will change
to use huge_ptep_clear_flush() instead in the following patches.

So this is a preparation patch, which changes the huge_ptep_clear_flush()
to return the original pte to help to nuke a hugetlb page table.

Signed-off-by: Baolin Wang <[e-mail]>
Acked-by: Mike Kravetz <[e-mail]>
---
 arch/arm64/include/asm/hugetlb.h   |  4 ++--
 arch/arm64/mm/hugetlbpage.c        | 12 +++++-------
 arch/ia64/include/asm/hugetlb.h    |  4 ++--
 arch/mips/include/asm/hugetlb.h    |  9 ++++++---
 arch/parisc/include/asm/hugetlb.h  |  4 ++--
 arch/powerpc/include/asm/hugetlb.h |  9 ++++++---
 arch/s390/include/asm/hugetlb.h    |  6 +++---
 arch/sh/include/asm/hugetlb.h      |  4 ++--
 arch/sparc/include/asm/hugetlb.h   |  4 ++--
 include/asm-generic/hugetlb.h      |  4 ++--
 mm/hugetlb.c                       |  2 +-
 11 files changed, 33 insertions(+), 29 deletions(-)

Comments

Muchun Song May 8, 2022, 11:09 a.m. UTC | #1

On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
> It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
> table when unmapping or migrating a hugetlb page, and will change
> to use huge_ptep_clear_flush() instead in the following patches.
> 
> So this is a preparation patch, which changes the huge_ptep_clear_flush()
> to return the original pte to help to nuke a hugetlb page table.
> 
> Signed-off-by: Baolin Wang <[e-mail]>
> Acked-by: Mike Kravetz <[e-mail]>

Reviewed-by: Muchun Song <[e-mail]>

But one nit below:

[...]
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 8605d7e..61a21af 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>  		ClearHPageRestoreReserve(new_page);
>  
>  		/* Break COW or unshare */
> -		huge_ptep_clear_flush(vma, haddr, ptep);
> +		(void)huge_ptep_clear_flush(vma, haddr, ptep);

Why add a "(void)" here? Is there any warning if no "(void)"?
IIUC, I think we can remove this, right?

>  		mmu_notifier_invalidate_range(mm, range.start, range.end);
>  		page_remove_rmap(old_page, vma, true);
>  		hugepage_add_new_anon_rmap(new_page, vma, haddr);
> -- 
> 1.8.3.1
> 
>

Baolin Wang May 8, 2022, 1:09 p.m. UTC | #2

On 5/8/2022 7:09 PM, Muchun Song wrote:
> On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
>> It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
>> table when unmapping or migrating a hugetlb page, and will change
>> to use huge_ptep_clear_flush() instead in the following patches.
>>
>> So this is a preparation patch, which changes the huge_ptep_clear_flush()
>> to return the original pte to help to nuke a hugetlb page table.
>>
>> Signed-off-by: Baolin Wang <[e-mail]>
>> Acked-by: Mike Kravetz <[e-mail]>
> 
> Reviewed-by: Muchun Song <[e-mail]>

Thanks for reviewing.

> 
> But one nit below:
> 
> [...]
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 8605d7e..61a21af 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>>   		ClearHPageRestoreReserve(new_page);
>>   
>>   		/* Break COW or unshare */
>> -		huge_ptep_clear_flush(vma, haddr, ptep);
>> +		(void)huge_ptep_clear_flush(vma, haddr, ptep);
> 
> Why add a "(void)" here? Is there any warning if no "(void)"?
> IIUC, I think we can remove this, right?

I did not meet any warning without the casting, but this is per Mike's 
comment[1] to make the code consistent with other functions casting to 
void type explicitly in hugetlb.c file.

[1] 
https://lore.kernel.org/all/[e-mail]/

Muchun Song May 9, 2022, 4:06 a.m. UTC | #3

On Sun, May 08, 2022 at 09:09:55PM +0800, Baolin Wang wrote:
> 
> 
> On 5/8/2022 7:09 PM, Muchun Song wrote:
> > On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
> > > It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
> > > table when unmapping or migrating a hugetlb page, and will change
> > > to use huge_ptep_clear_flush() instead in the following patches.
> > > 
> > > So this is a preparation patch, which changes the huge_ptep_clear_flush()
> > > to return the original pte to help to nuke a hugetlb page table.
> > > 
> > > Signed-off-by: Baolin Wang <[e-mail]>
> > > Acked-by: Mike Kravetz <[e-mail]>
> > 
> > Reviewed-by: Muchun Song <[e-mail]>
> 
> Thanks for reviewing.
> 
> > 
> > But one nit below:
> > 
> > [...]
> > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > > index 8605d7e..61a21af 100644
> > > --- a/mm/hugetlb.c
> > > +++ b/mm/hugetlb.c
> > > @@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
> > >   		ClearHPageRestoreReserve(new_page);
> > >   		/* Break COW or unshare */
> > > -		huge_ptep_clear_flush(vma, haddr, ptep);
> > > +		(void)huge_ptep_clear_flush(vma, haddr, ptep);
> > 
> > Why add a "(void)" here? Is there any warning if no "(void)"?
> > IIUC, I think we can remove this, right?
> 
> I did not meet any warning without the casting, but this is per Mike's
> comment[1] to make the code consistent with other functions casting to void
> type explicitly in hugetlb.c file.
>

Got it. I see hugetlb.c per this rule, while others do not.
 
> [1]
> https://lore.kernel.org/all/[e-mail]/
>

Christophe Leroy May 9, 2022, 5:46 a.m. UTC | #4

Le 08/05/2022 à 15:09, Baolin Wang a écrit :
> 
> 
> On 5/8/2022 7:09 PM, Muchun Song wrote:
>> On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
>>> It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
>>> table when unmapping or migrating a hugetlb page, and will change
>>> to use huge_ptep_clear_flush() instead in the following patches.
>>>
>>> So this is a preparation patch, which changes the 
>>> huge_ptep_clear_flush()
>>> to return the original pte to help to nuke a hugetlb page table.
>>>
>>> Signed-off-by: Baolin Wang <[e-mail]>
>>> Acked-by: Mike Kravetz <[e-mail]>
>>
>> Reviewed-by: Muchun Song <[e-mail]>
> 
> Thanks for reviewing.
> 
>>
>> But one nit below:
>>
>> [...]
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index 8605d7e..61a21af 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct 
>>> *mm, struct vm_area_struct *vma,
>>>           ClearHPageRestoreReserve(new_page);
>>>           /* Break COW or unshare */
>>> -        huge_ptep_clear_flush(vma, haddr, ptep);
>>> +        (void)huge_ptep_clear_flush(vma, haddr, ptep);
>>
>> Why add a "(void)" here? Is there any warning if no "(void)"?
>> IIUC, I think we can remove this, right?
> 
> I did not meet any warning without the casting, but this is per Mike's 
> comment[1] to make the code consistent with other functions casting to 
> void type explicitly in hugetlb.c file.
> 
> [1] 
> https://lore.kernel.org/all/[e-mail]/ 
> 

As far as I understand, Mike said that you should be accompagnied with a 
big fat comment explaining why we ignore the returned value from 
huge_ptep_clear_flush().

By the way huge_ptep_clear_flush() is not declared 'must_check' so this 
cast is just visual polution and should be removed.

In the meantime the comment suggested by Mike should be added instead.

Christophe

Baolin Wang May 9, 2022, 8:46 a.m. UTC | #5

On 5/9/2022 1:46 PM, Christophe Leroy wrote:
> 
> 
> Le 08/05/2022 à 15:09, Baolin Wang a écrit :
>>
>>
>> On 5/8/2022 7:09 PM, Muchun Song wrote:
>>> On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
>>>> It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
>>>> table when unmapping or migrating a hugetlb page, and will change
>>>> to use huge_ptep_clear_flush() instead in the following patches.
>>>>
>>>> So this is a preparation patch, which changes the
>>>> huge_ptep_clear_flush()
>>>> to return the original pte to help to nuke a hugetlb page table.
>>>>
>>>> Signed-off-by: Baolin Wang <[e-mail]>
>>>> Acked-by: Mike Kravetz <[e-mail]>
>>>
>>> Reviewed-by: Muchun Song <[e-mail]>
>>
>> Thanks for reviewing.
>>
>>>
>>> But one nit below:
>>>
>>> [...]
>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>>> index 8605d7e..61a21af 100644
>>>> --- a/mm/hugetlb.c
>>>> +++ b/mm/hugetlb.c
>>>> @@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct
>>>> *mm, struct vm_area_struct *vma,
>>>>            ClearHPageRestoreReserve(new_page);
>>>>            /* Break COW or unshare */
>>>> -        huge_ptep_clear_flush(vma, haddr, ptep);
>>>> +        (void)huge_ptep_clear_flush(vma, haddr, ptep);
>>>
>>> Why add a "(void)" here? Is there any warning if no "(void)"?
>>> IIUC, I think we can remove this, right?
>>
>> I did not meet any warning without the casting, but this is per Mike's
>> comment[1] to make the code consistent with other functions casting to
>> void type explicitly in hugetlb.c file.
>>
>> [1]
>> https://lore.kernel.org/all/[e-mail]/
>>
> 
> As far as I understand, Mike said that you should be accompagnied with a
> big fat comment explaining why we ignore the returned value from
> huge_ptep_clear_flush(). >
> By the way huge_ptep_clear_flush() is not declared 'must_check' so this
> cast is just visual polution and should be removed.
> 
> In the meantime the comment suggested by Mike should be added instead.
Sorry for my misunderstanding. I just follow the explicit void casting 
like other places in hugetlb.c file. And I am not sure if it is useful 
adding some comments like below, since we did not need the original pte 
value in the COW case mapping with a new page, and the code is more 
readable already I think.

Mike, could you help to clarify what useful comments would you like? and 
remove the explicit void casting? Thanks.

/*
  * Just ignore the return value with new page mapped.
  */

Mike Kravetz May 9, 2022, 8:02 p.m. UTC | #6

On 5/9/22 01:46, Baolin Wang wrote:
> 
> 
> On 5/9/2022 1:46 PM, Christophe Leroy wrote:
>>
>>
>> Le 08/05/2022 à 15:09, Baolin Wang a écrit :
>>>
>>>
>>> On 5/8/2022 7:09 PM, Muchun Song wrote:
>>>> On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
>>>>> It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
>>>>> table when unmapping or migrating a hugetlb page, and will change
>>>>> to use huge_ptep_clear_flush() instead in the following patches.
>>>>>
>>>>> So this is a preparation patch, which changes the
>>>>> huge_ptep_clear_flush()
>>>>> to return the original pte to help to nuke a hugetlb page table.
>>>>>
>>>>> Signed-off-by: Baolin Wang <[e-mail]>
>>>>> Acked-by: Mike Kravetz <[e-mail]>
>>>>
>>>> Reviewed-by: Muchun Song <[e-mail]>
>>>
>>> Thanks for reviewing.
>>>
>>>>
>>>> But one nit below:
>>>>
>>>> [...]
>>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>>>> index 8605d7e..61a21af 100644
>>>>> --- a/mm/hugetlb.c
>>>>> +++ b/mm/hugetlb.c
>>>>> @@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct
>>>>> *mm, struct vm_area_struct *vma,
>>>>>            ClearHPageRestoreReserve(new_page);
>>>>>            /* Break COW or unshare */
>>>>> -        huge_ptep_clear_flush(vma, haddr, ptep);
>>>>> +        (void)huge_ptep_clear_flush(vma, haddr, ptep);
>>>>
>>>> Why add a "(void)" here? Is there any warning if no "(void)"?
>>>> IIUC, I think we can remove this, right?
>>>
>>> I did not meet any warning without the casting, but this is per Mike's
>>> comment[1] to make the code consistent with other functions casting to
>>> void type explicitly in hugetlb.c file.
>>>
>>> [1]
>>> https://lore.kernel.org/all/[e-mail]/
>>>
>>
>> As far as I understand, Mike said that you should be accompagnied with a
>> big fat comment explaining why we ignore the returned value from
>> huge_ptep_clear_flush(). >
>> By the way huge_ptep_clear_flush() is not declared 'must_check' so this
>> cast is just visual polution and should be removed.
>>
>> In the meantime the comment suggested by Mike should be added instead.
> Sorry for my misunderstanding. I just follow the explicit void casting like other places in hugetlb.c file. And I am not sure if it is useful adding some comments like below, since we did not need the original pte value in the COW case mapping with a new page, and the code is more readable already I think.
> 
> Mike, could you help to clarify what useful comments would you like? and remove the explicit void casting? Thanks.
> 

Sorry for the confusion.

In the original commit, it seemed odd to me that the signature of the
function was changing and there was not an associated change to the only
caller of the function.  I did suggest casting to void or adding a comment.
As Christophe mentions, the cast to void is not necessary.  In addition,
there really isn't a need for a comment as the calling code is not changed.

The original version of the commit without either is actually preferable.
The commit message does say this is a preparation patch and the return
value will be used in later patches.
Again, sorry for the confusion.

Baolin Wang May 10, 2022, 1:35 a.m. UTC | #7

On 5/10/2022 4:02 AM, Mike Kravetz wrote:
> On 5/9/22 01:46, Baolin Wang wrote:
>>
>>
>> On 5/9/2022 1:46 PM, Christophe Leroy wrote:
>>>
>>>
>>> Le 08/05/2022 à 15:09, Baolin Wang a écrit :
>>>>
>>>>
>>>> On 5/8/2022 7:09 PM, Muchun Song wrote:
>>>>> On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
>>>>>> It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
>>>>>> table when unmapping or migrating a hugetlb page, and will change
>>>>>> to use huge_ptep_clear_flush() instead in the following patches.
>>>>>>
>>>>>> So this is a preparation patch, which changes the
>>>>>> huge_ptep_clear_flush()
>>>>>> to return the original pte to help to nuke a hugetlb page table.
>>>>>>
>>>>>> Signed-off-by: Baolin Wang <[e-mail]>
>>>>>> Acked-by: Mike Kravetz <[e-mail]>
>>>>>
>>>>> Reviewed-by: Muchun Song <[e-mail]>
>>>>
>>>> Thanks for reviewing.
>>>>
>>>>>
>>>>> But one nit below:
>>>>>
>>>>> [...]
>>>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>>>>> index 8605d7e..61a21af 100644
>>>>>> --- a/mm/hugetlb.c
>>>>>> +++ b/mm/hugetlb.c
>>>>>> @@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct
>>>>>> *mm, struct vm_area_struct *vma,
>>>>>>             ClearHPageRestoreReserve(new_page);
>>>>>>             /* Break COW or unshare */
>>>>>> -        huge_ptep_clear_flush(vma, haddr, ptep);
>>>>>> +        (void)huge_ptep_clear_flush(vma, haddr, ptep);
>>>>>
>>>>> Why add a "(void)" here? Is there any warning if no "(void)"?
>>>>> IIUC, I think we can remove this, right?
>>>>
>>>> I did not meet any warning without the casting, but this is per Mike's
>>>> comment[1] to make the code consistent with other functions casting to
>>>> void type explicitly in hugetlb.c file.
>>>>
>>>> [1]
>>>> https://lore.kernel.org/all/[e-mail]/
>>>>
>>>
>>> As far as I understand, Mike said that you should be accompagnied with a
>>> big fat comment explaining why we ignore the returned value from
>>> huge_ptep_clear_flush(). >
>>> By the way huge_ptep_clear_flush() is not declared 'must_check' so this
>>> cast is just visual polution and should be removed.
>>>
>>> In the meantime the comment suggested by Mike should be added instead.
>> Sorry for my misunderstanding. I just follow the explicit void casting like other places in hugetlb.c file. And I am not sure if it is useful adding some comments like below, since we did not need the original pte value in the COW case mapping with a new page, and the code is more readable already I think.
>>
>> Mike, could you help to clarify what useful comments would you like? and remove the explicit void casting? Thanks.
>>
> 
> Sorry for the confusion.
> 
> In the original commit, it seemed odd to me that the signature of the
> function was changing and there was not an associated change to the only
> caller of the function.  I did suggest casting to void or adding a comment.
> As Christophe mentions, the cast to void is not necessary.  In addition,
> there really isn't a need for a comment as the calling code is not changed.

OK. Will drop the casting in next version.

> 
> The original version of the commit without either is actually preferable.
> The commit message does say this is a preparation patch and the return
> value will be used in later patches.

OK. Thanks Mike for making me clear. Also thanks to Muchun and Christophe.

Patch

diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
index 1242f71..616b2ca 100644
--- a/arch/arm64/include/asm/hugetlb.h
+++ b/arch/arm64/include/asm/hugetlb.h
@@ -39,8 +39,8 @@  extern pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
 extern void huge_ptep_set_wrprotect(struct mm_struct *mm,
 				    unsigned long addr, pte_t *ptep);
 #define __HAVE_ARCH_HUGE_PTEP_CLEAR_FLUSH
-extern void huge_ptep_clear_flush(struct vm_area_struct *vma,
-				  unsigned long addr, pte_t *ptep);
+extern pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
+				   unsigned long addr, pte_t *ptep);
 #define __HAVE_ARCH_HUGE_PTE_CLEAR
 extern void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
 			   pte_t *ptep, unsigned long sz);
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index cbace1c..ca8e65c 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -486,19 +486,17 @@  void huge_ptep_set_wrprotect(struct mm_struct *mm,
 		set_pte_at(mm, addr, ptep, pfn_pte(pfn, hugeprot));
 }
 
-void huge_ptep_clear_flush(struct vm_area_struct *vma,
-			   unsigned long addr, pte_t *ptep)
+pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
+			    unsigned long addr, pte_t *ptep)
 {
 	size_t pgsize;
 	int ncontig;
 
-	if (!pte_cont(READ_ONCE(*ptep))) {
-		ptep_clear_flush(vma, addr, ptep);
-		return;
-	}
+	if (!pte_cont(READ_ONCE(*ptep)))
+		return ptep_clear_flush(vma, addr, ptep);
 
 	ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize);
-	clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig);
+	return get_clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig);
 }
 
 static int __init hugetlbpage_init(void)
diff --git a/arch/ia64/include/asm/hugetlb.h b/arch/ia64/include/asm/hugetlb.h
index 7e46ebd..65d3811 100644
--- a/arch/ia64/include/asm/hugetlb.h
+++ b/arch/ia64/include/asm/hugetlb.h
@@ -23,8 +23,8 @@  static inline int is_hugepage_only_range(struct mm_struct *mm,
 #define is_hugepage_only_range is_hugepage_only_range
 
 #define __HAVE_ARCH_HUGE_PTEP_CLEAR_FLUSH
-static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
-					 unsigned long addr, pte_t *ptep)
+static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
+					  unsigned long addr, pte_t *ptep)
 {
 }
 
diff --git a/arch/mips/include/asm/hugetlb.h b/arch/mips/include/asm/hugetlb.h
index c214440..fd69c88 100644
--- a/arch/mips/include/asm/hugetlb.h
+++ b/arch/mips/include/asm/hugetlb.h
@@ -43,16 +43,19 @@  static inline pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
 }
 
 #define __HAVE_ARCH_HUGE_PTEP_CLEAR_FLUSH
-static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
-					 unsigned long addr, pte_t *ptep)
+static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
+					  unsigned long addr, pte_t *ptep)
 {
+	pte_t pte;
+
 	/*
 	 * clear the huge pte entry firstly, so that the other smp threads will
 	 * not get old pte entry after finishing flush_tlb_page and before
 	 * setting new huge pte entry
 	 */
-	huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
+	pte = huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
 	flush_tlb_page(vma, addr);
+	return pte;
 }
 
 #define __HAVE_ARCH_HUGE_PTE_NONE
diff --git a/arch/parisc/include/asm/hugetlb.h b/arch/parisc/include/asm/hugetlb.h
index a69cf9e..25bc560 100644
--- a/arch/parisc/include/asm/hugetlb.h
+++ b/arch/parisc/include/asm/hugetlb.h
@@ -28,8 +28,8 @@  static inline int prepare_hugepage_range(struct file *file,
 }
 
 #define __HAVE_ARCH_HUGE_PTEP_CLEAR_FLUSH
-static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
-					 unsigned long addr, pte_t *ptep)
+static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
+					  unsigned long addr, pte_t *ptep)
 {
 }
 
diff --git a/arch/powerpc/include/asm/hugetlb.h b/arch/powerpc/include/asm/hugetlb.h
index 6a1a1ac..8a5674f 100644
--- a/arch/powerpc/include/asm/hugetlb.h
+++ b/arch/powerpc/include/asm/hugetlb.h
@@ -43,11 +43,14 @@  static inline pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
 }
 
 #define __HAVE_ARCH_HUGE_PTEP_CLEAR_FLUSH
-static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
-					 unsigned long addr, pte_t *ptep)
+static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
+					  unsigned long addr, pte_t *ptep)
 {
-	huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
+	pte_t pte;
+
+	pte = huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
 	flush_hugetlb_page(vma, addr);
+	return pte;
 }
 
 #define __HAVE_ARCH_HUGE_PTEP_SET_ACCESS_FLAGS
diff --git a/arch/s390/include/asm/hugetlb.h b/arch/s390/include/asm/hugetlb.h
index 32c3fd6..f22beda 100644
--- a/arch/s390/include/asm/hugetlb.h
+++ b/arch/s390/include/asm/hugetlb.h
@@ -50,10 +50,10 @@  static inline void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
 		set_pte(ptep, __pte(_SEGMENT_ENTRY_EMPTY));
 }
 
-static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
-					 unsigned long address, pte_t *ptep)
+static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
+					  unsigned long address, pte_t *ptep)
 {
-	huge_ptep_get_and_clear(vma->vm_mm, address, ptep);
+	return huge_ptep_get_and_clear(vma->vm_mm, address, ptep);
 }
 
 static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma,
diff --git a/arch/sh/include/asm/hugetlb.h b/arch/sh/include/asm/hugetlb.h
index ae4de7b..e727cc9 100644
--- a/arch/sh/include/asm/hugetlb.h
+++ b/arch/sh/include/asm/hugetlb.h
@@ -21,8 +21,8 @@  static inline int prepare_hugepage_range(struct file *file,
 }
 
 #define __HAVE_ARCH_HUGE_PTEP_CLEAR_FLUSH
-static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
-					 unsigned long addr, pte_t *ptep)
+static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
+					  unsigned long addr, pte_t *ptep)
 {
 }
 
diff --git a/arch/sparc/include/asm/hugetlb.h b/arch/sparc/include/asm/hugetlb.h
index 53838a1..b50aa6f 100644
--- a/arch/sparc/include/asm/hugetlb.h
+++ b/arch/sparc/include/asm/hugetlb.h
@@ -21,8 +21,8 @@  pte_t huge_ptep_get_and_clear(struct mm_struct *mm, unsigned long addr,
 			      pte_t *ptep);
 
 #define __HAVE_ARCH_HUGE_PTEP_CLEAR_FLUSH
-static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
-					 unsigned long addr, pte_t *ptep)
+static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
+					  unsigned long addr, pte_t *ptep)
 {
 }
 
diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h
index 896f341..a57d667 100644
--- a/include/asm-generic/hugetlb.h
+++ b/include/asm-generic/hugetlb.h
@@ -84,10 +84,10 @@  static inline pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
 #endif
 
 #ifndef __HAVE_ARCH_HUGE_PTEP_CLEAR_FLUSH
-static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
+static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
 		unsigned long addr, pte_t *ptep)
 {
-	ptep_clear_flush(vma, addr, ptep);
+	return ptep_clear_flush(vma, addr, ptep);
 }
 #endif
 
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8605d7e..61a21af 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5342,7 +5342,7 @@  static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
 		ClearHPageRestoreReserve(new_page);
 
 		/* Break COW or unshare */
-		huge_ptep_clear_flush(vma, haddr, ptep);
+		(void)huge_ptep_clear_flush(vma, haddr, ptep);
 		mmu_notifier_invalidate_range(mm, range.start, range.end);
 		page_remove_rmap(old_page, vma, true);
 		hugepage_add_new_anon_rmap(new_page, vma, haddr);