[PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[j.glisse]

From: Jerome Glisse <jglisse@redhat.com>

Do not increase page count if FOLL_GET is not set. None of the
current user can trigger the issue because none of the current
user call __get_user_pages with both the pages array ptr non
NULL and the FOLL_GET flags non set in other word all caller
of __get_user_pages that don't set the FOLL_GET flags also call
with pages == NULL.

v2: Do not use get_page_foll. Improved comment.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
---
 mm/hugetlb.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ca9a7c6..32f323b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2981,7 +2981,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 same_page:
 		if (pages) {
 			pages[i] = mem_map_offset(page, pfn_offset);
-			get_page(pages[i]);
+			if (flags & FOLL_GET) {
+				get_page(pages[i]);
+			}
 		}
 
 		if (vmas)
-- 
1.7.11.7

[PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[j.glisse]

From: Jerome Glisse <jglisse@redhat.com>

Do not increase page count if FOLL_GET is not set. None of the
current user can trigger the issue because none of the current
user call __get_user_pages with both the pages array ptr non
NULL and the FOLL_GET flags non set in other word all caller
of __get_user_pages that don't set the FOLL_GET flags also call
with pages == NULL.

v2: Do not use get_page_foll. Improved comment.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
---
 mm/hugetlb.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ca9a7c6..32f323b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2981,7 +2981,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 same_page:
 		if (pages) {
 			pages[i] = mem_map_offset(page, pfn_offset);
-			get_page(pages[i]);
+			if (flags & FOLL_GET) {
+				get_page(pages[i]);
+			}
 		}
 
 		if (vmas)
-- 
1.7.11.7

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Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[KOSAKI Motohiro]

On Tue, May 7, 2013 at 6:58 PM,  <j.glisse@gmail.com> wrote:
> From: Jerome Glisse <jglisse@redhat.com>
>
> Do not increase page count if FOLL_GET is not set. None of the
> current user can trigger the issue because none of the current
> user call __get_user_pages with both the pages array ptr non
> NULL and the FOLL_GET flags non set in other word all caller
> of __get_user_pages that don't set the FOLL_GET flags also call
> with pages == NULL.

Because, __get_user_pages() doesn't allow pages==NULL and FOLL_GET is on.


long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
{
(snip)
    VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[KOSAKI Motohiro]

On Tue, May 7, 2013 at 6:58 PM,  <j.glisse@gmail.com> wrote:
> From: Jerome Glisse <jglisse@redhat.com>
>
> Do not increase page count if FOLL_GET is not set. None of the
> current user can trigger the issue because none of the current
> user call __get_user_pages with both the pages array ptr non
> NULL and the FOLL_GET flags non set in other word all caller
> of __get_user_pages that don't set the FOLL_GET flags also call
> with pages == NULL.

Because, __get_user_pages() doesn't allow pages==NULL and FOLL_GET is on.


long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
{
(snip)
    VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

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Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[Jerome Glisse]

On Tue, May 7, 2013 at 8:47 PM, KOSAKI Motohiro
<kosaki.motohiro@gmail.com> wrote:
> On Tue, May 7, 2013 at 6:58 PM,  <j.glisse@gmail.com> wrote:
>> From: Jerome Glisse <jglisse@redhat.com>
>>
>> Do not increase page count if FOLL_GET is not set. None of the
>> current user can trigger the issue because none of the current
>> user call __get_user_pages with both the pages array ptr non
>> NULL and the FOLL_GET flags non set in other word all caller
>> of __get_user_pages that don't set the FOLL_GET flags also call
>> with pages == NULL.
>
> Because, __get_user_pages() doesn't allow pages==NULL and FOLL_GET is on.

Yes but this allow pages != NULL and FOLL_GET not set and as i said
there is no such user of that yet and this is exactly what i was
trying to use.

Cheers,
Jerome

>
> long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> {
> (snip)
>     VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[Jerome Glisse]

On Tue, May 7, 2013 at 8:47 PM, KOSAKI Motohiro
<kosaki.motohiro@gmail.com> wrote:
> On Tue, May 7, 2013 at 6:58 PM,  <j.glisse@gmail.com> wrote:
>> From: Jerome Glisse <jglisse@redhat.com>
>>
>> Do not increase page count if FOLL_GET is not set. None of the
>> current user can trigger the issue because none of the current
>> user call __get_user_pages with both the pages array ptr non
>> NULL and the FOLL_GET flags non set in other word all caller
>> of __get_user_pages that don't set the FOLL_GET flags also call
>> with pages == NULL.
>
> Because, __get_user_pages() doesn't allow pages==NULL and FOLL_GET is on.

Yes but this allow pages != NULL and FOLL_GET not set and as i said
there is no such user of that yet and this is exactly what i was
trying to use.

Cheers,
Jerome

>
> long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> {
> (snip)
>     VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

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Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[KOSAKI Motohiro]

On Tue, May 7, 2013 at 8:51 PM, Jerome Glisse <j.glisse@gmail.com> wrote:
> On Tue, May 7, 2013 at 8:47 PM, KOSAKI Motohiro
> <kosaki.motohiro@gmail.com> wrote:
>> On Tue, May 7, 2013 at 6:58 PM,  <j.glisse@gmail.com> wrote:
>>> From: Jerome Glisse <jglisse@redhat.com>
>>>
>>> Do not increase page count if FOLL_GET is not set. None of the
>>> current user can trigger the issue because none of the current
>>> user call __get_user_pages with both the pages array ptr non
>>> NULL and the FOLL_GET flags non set in other word all caller
>>> of __get_user_pages that don't set the FOLL_GET flags also call
>>> with pages == NULL.
>>
>> Because, __get_user_pages() doesn't allow pages==NULL and FOLL_GET is on.
>
> Yes but this allow pages != NULL and FOLL_GET not set and as i said
> there is no such user of that yet and this is exactly what i was
> trying to use.

Why? The following bug_on inhibit both case.

>>     VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[KOSAKI Motohiro]

On Tue, May 7, 2013 at 8:51 PM, Jerome Glisse <j.glisse@gmail.com> wrote:
> On Tue, May 7, 2013 at 8:47 PM, KOSAKI Motohiro
> <kosaki.motohiro@gmail.com> wrote:
>> On Tue, May 7, 2013 at 6:58 PM,  <j.glisse@gmail.com> wrote:
>>> From: Jerome Glisse <jglisse@redhat.com>
>>>
>>> Do not increase page count if FOLL_GET is not set. None of the
>>> current user can trigger the issue because none of the current
>>> user call __get_user_pages with both the pages array ptr non
>>> NULL and the FOLL_GET flags non set in other word all caller
>>> of __get_user_pages that don't set the FOLL_GET flags also call
>>> with pages == NULL.
>>
>> Because, __get_user_pages() doesn't allow pages==NULL and FOLL_GET is on.
>
> Yes but this allow pages != NULL and FOLL_GET not set and as i said
> there is no such user of that yet and this is exactly what i was
> trying to use.

Why? The following bug_on inhibit both case.

>>     VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

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Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[Jerome Glisse]

On Tue, May 7, 2013 at 10:41 PM, KOSAKI Motohiro
<kosaki.motohiro@gmail.com> wrote:
> On Tue, May 7, 2013 at 8:51 PM, Jerome Glisse <j.glisse@gmail.com> wrote:
>> On Tue, May 7, 2013 at 8:47 PM, KOSAKI Motohiro
>> <kosaki.motohiro@gmail.com> wrote:
>>> On Tue, May 7, 2013 at 6:58 PM,  <j.glisse@gmail.com> wrote:
>>>> From: Jerome Glisse <jglisse@redhat.com>
>>>>
>>>> Do not increase page count if FOLL_GET is not set. None of the
>>>> current user can trigger the issue because none of the current
>>>> user call __get_user_pages with both the pages array ptr non
>>>> NULL and the FOLL_GET flags non set in other word all caller
>>>> of __get_user_pages that don't set the FOLL_GET flags also call
>>>> with pages == NULL.
>>>
>>> Because, __get_user_pages() doesn't allow pages==NULL and FOLL_GET is on.
>>
>> Yes but this allow pages != NULL and FOLL_GET not set and as i said
>> there is no such user of that yet and this is exactly what i was
>> trying to use.
>
> Why? The following bug_on inhibit both case.

Yes i get lost on the double negation, but still my patch is correct
and i am not using gup but follow_hugetlb_page directly and i run into
the issue. My patch does not change the behavior for current user,
just fix assumption new user might have when not setting the FOLL_GET
flags.

>>>     VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[Jerome Glisse]

On Tue, May 7, 2013 at 10:41 PM, KOSAKI Motohiro
<kosaki.motohiro@gmail.com> wrote:
> On Tue, May 7, 2013 at 8:51 PM, Jerome Glisse <j.glisse@gmail.com> wrote:
>> On Tue, May 7, 2013 at 8:47 PM, KOSAKI Motohiro
>> <kosaki.motohiro@gmail.com> wrote:
>>> On Tue, May 7, 2013 at 6:58 PM,  <j.glisse@gmail.com> wrote:
>>>> From: Jerome Glisse <jglisse@redhat.com>
>>>>
>>>> Do not increase page count if FOLL_GET is not set. None of the
>>>> current user can trigger the issue because none of the current
>>>> user call __get_user_pages with both the pages array ptr non
>>>> NULL and the FOLL_GET flags non set in other word all caller
>>>> of __get_user_pages that don't set the FOLL_GET flags also call
>>>> with pages == NULL.
>>>
>>> Because, __get_user_pages() doesn't allow pages==NULL and FOLL_GET is on.
>>
>> Yes but this allow pages != NULL and FOLL_GET not set and as i said
>> there is no such user of that yet and this is exactly what i was
>> trying to use.
>
> Why? The following bug_on inhibit both case.

Yes i get lost on the double negation, but still my patch is correct
and i am not using gup but follow_hugetlb_page directly and i run into
the issue. My patch does not change the behavior for current user,
just fix assumption new user might have when not setting the FOLL_GET
flags.

>>>     VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

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Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[KOSAKI Motohiro]

>> Why? The following bug_on inhibit both case.
>
> Yes i get lost on the double negation, but still my patch is correct
> and i am not using gup but follow_hugetlb_page directly and i run into
> the issue. My patch does not change the behavior for current user,
> just fix assumption new user might have when not setting the FOLL_GET
> flags.

I have no idea. I haven't seen your new use case.

Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[KOSAKI Motohiro]

>> Why? The following bug_on inhibit both case.
>
> Yes i get lost on the double negation, but still my patch is correct
> and i am not using gup but follow_hugetlb_page directly and i run into
> the issue. My patch does not change the behavior for current user,
> just fix assumption new user might have when not setting the FOLL_GET
> flags.

I have no idea. I haven't seen your new use case.

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