Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-10-16 Thread zhong jiang 
On 2019/10/17 8:49, Andrew Morton wrote:
> On Wed, 16 Oct 2019 17:07:44 +0800 zhong jiang  wrote:
>
 --- a/mm/gup.c~a
 +++ a/mm/gup.c
 @@ -1450,6 +1450,7 @@ static long check_and_migrate_cma_pages(
   bool drain_allow = true;
   bool migrate_allow = true;
   LIST_HEAD(cma_page_list);
 +long ret;
 check_again:
   for (i = 0; i < nr_pages;) {
 @@ -1511,17 +1512,18 @@ check_again:
* again migrating any new CMA pages which we failed to isolate
* earlier.
*/
 -nr_pages = __get_user_pages_locked(tsk, mm, start, nr_pages,
 +ret = __get_user_pages_locked(tsk, mm, start, nr_pages,
  pages, vmas, NULL,
  gup_flags);
   -if ((nr_pages > 0) && migrate_allow) {
 +nr_pages = ret;
 +if (ret > 0 && migrate_allow) {
   drain_allow = true;
   goto check_again;
   }
   }
   -return nr_pages;
 +return ret;
   }
   #else
   static long check_and_migrate_cma_pages(struct task_struct *tsk,

>>> +1 for this approach, please.
>>>
>>>
>>> thanks,
>> Hi,  Andrew
>>
>> I didn't see the fix for the issue in the upstream. Your proposal should be
>> appiled to upstream. Could you appiled the patch or  repost by me ?
> Forgotten about it ;)  Please send a patch sometime?
>
> .
>
I will  repost the patch as your suggestion.  Thanks,

Sincerely,
zhong jiang

Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-10-16 Thread Andrew Morton 
On Wed, 16 Oct 2019 17:07:44 +0800 zhong jiang  wrote:

> >> --- a/mm/gup.c~a
> >> +++ a/mm/gup.c
> >> @@ -1450,6 +1450,7 @@ static long check_and_migrate_cma_pages(
> >>   bool drain_allow = true;
> >>   bool migrate_allow = true;
> >>   LIST_HEAD(cma_page_list);
> >> +long ret;
> >> check_again:
> >>   for (i = 0; i < nr_pages;) {
> >> @@ -1511,17 +1512,18 @@ check_again:
> >>* again migrating any new CMA pages which we failed to isolate
> >>* earlier.
> >>*/
> >> -nr_pages = __get_user_pages_locked(tsk, mm, start, nr_pages,
> >> +ret = __get_user_pages_locked(tsk, mm, start, nr_pages,
> >>  pages, vmas, NULL,
> >>  gup_flags);
> >>   -if ((nr_pages > 0) && migrate_allow) {
> >> +nr_pages = ret;
> >> +if (ret > 0 && migrate_allow) {
> >>   drain_allow = true;
> >>   goto check_again;
> >>   }
> >>   }
> >>   -return nr_pages;
> >> +return ret;
> >>   }
> >>   #else
> >>   static long check_and_migrate_cma_pages(struct task_struct *tsk,
> >>
> >
> > +1 for this approach, please.
> >
> >
> > thanks,
> Hi,  Andrew
> 
> I didn't see the fix for the issue in the upstream. Your proposal should be
> appiled to upstream. Could you appiled the patch or  repost by me ?

Forgotten about it ;)  Please send a patch sometime?

Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-09-05 Thread Vlastimil Babka 
On 9/5/19 8:18 AM, zhong jiang wrote:
> On 2019/9/5 2:48, Andrew Morton wrote:
> Firstly,  I consider the some modified method as you has writen down above.  
> It seems to work well.
> According to Vlastimil's feedback,   I repost the patch in v2,   changing the 
> parameter to long to fix
> the issue.  which one do you prefer?

Please forget about my suggestion to change parameter to long, it was
wrong. New variable is better.

> Thanks,
> zhong jiang
>

Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-09-05 Thread zhong jiang 
On 2019/9/5 2:48, Andrew Morton wrote:
> On Wed, 4 Sep 2019 13:24:58 +0200 Vlastimil Babka  wrote:
>
>> On 9/4/19 12:26 PM, zhong jiang wrote:
>>> With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
>>> compare with zero. And __get_user_pages_locked will return an long value.
>>> Hence, Convert the long to compare with zero is feasible.
>> It would be nicer if the parameter nr_pages was long again instead of 
>> unsigned
>> long (note there are two variants of the function, so both should be 
>> changed).
> nr_pages should be unsigned - it's a count of pages!
>
> The bug is that __get_user_pages_locked() returns a signed long which
> can be a -ve errno.
>
> I think it's best if __get_user_pages_locked() is to get itself a new
> local with the same type as its return value.  Something like:
>
> --- a/mm/gup.c~a
> +++ a/mm/gup.c
> @@ -1450,6 +1450,7 @@ static long check_and_migrate_cma_pages(
>   bool drain_allow = true;
>   bool migrate_allow = true;
>   LIST_HEAD(cma_page_list);
> + long ret;
>  
>  check_again:
>   for (i = 0; i < nr_pages;) {
> @@ -1511,17 +1512,18 @@ check_again:
>* again migrating any new CMA pages which we failed to isolate
>* earlier.
>*/
> - nr_pages = __get_user_pages_locked(tsk, mm, start, nr_pages,
> + ret = __get_user_pages_locked(tsk, mm, start, nr_pages,
>  pages, vmas, NULL,
>  gup_flags);
>  
> - if ((nr_pages > 0) && migrate_allow) {
> + nr_pages = ret;
> + if (ret > 0 && migrate_allow) {
>   drain_allow = true;
>   goto check_again;
>   }
>   }
>  
> - return nr_pages;
> + return ret;
>  }
>  #else
>  static long check_and_migrate_cma_pages(struct task_struct *tsk,
Firstly,  I consider the some modified method as you has writen down above.  It 
seems to work well.
According to Vlastimil's feedback,   I repost the patch in v2,   changing the 
parameter to long to fix
the issue.  which one do you prefer?

Thanks,
zhong jiang

Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-09-04 Thread zhong jiang 
On 2019/9/4 19:24, Vlastimil Babka wrote:
> On 9/4/19 12:26 PM, zhong jiang wrote:
>> With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
>> compare with zero. And __get_user_pages_locked will return an long value.
>> Hence, Convert the long to compare with zero is feasible.
> It would be nicer if the parameter nr_pages was long again instead of unsigned
> long (note there are two variants of the function, so both should be changed).
Yep, the parameter 'nr_pages' was changed to long. and the variants ‘i、step’ 
should
be changed accordingly.
>> Signed-off-by: zhong jiang 
> Fixes: 932f4a630a69 ("mm/gup: replace get_user_pages_longterm() with 
> FOLL_LONGTERM")
>
> (which changed long to unsigned long)
>
> AFAICS... stable shouldn't be needed as the only "risk" is that we goto
> check_again even when we fail, which should be harmless.
Agreed, Thanks.

Sincerely,
zhong jiang
> Vlastimil
>
>> ---
>>  mm/gup.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/gup.c b/mm/gup.c
>> index 23a9f9c..956d5a1 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -1508,7 +1508,7 @@ static long check_and_migrate_cma_pages(struct 
>> task_struct *tsk,
>> pages, vmas, NULL,
>> gup_flags);
>>  
>> -if ((nr_pages > 0) && migrate_allow) {
>> +if (((long)nr_pages > 0) && migrate_allow) {
>>  drain_allow = true;
>>  goto check_again;
>>  }
>>
>
> .
>

Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-09-04 Thread Vlastimil Babka 
On 9/4/19 9:01 PM, Andrew Morton wrote:
> On Wed, 4 Sep 2019 13:24:58 +0200 Vlastimil Babka  wrote:
> 
>> On 9/4/19 12:26 PM, zhong jiang wrote:
>>> With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
>>> compare with zero. And __get_user_pages_locked will return an long value.
>>> Hence, Convert the long to compare with zero is feasible.
>>
>> It would be nicer if the parameter nr_pages was long again instead of 
>> unsigned
>> long (note there are two variants of the function, so both should be 
>> changed).
>>
>>> Signed-off-by: zhong jiang 
>>
>> Fixes: 932f4a630a69 ("mm/gup: replace get_user_pages_longterm() with 
>> FOLL_LONGTERM")
>>
>> (which changed long to unsigned long)
>>
>> AFAICS... stable shouldn't be needed as the only "risk" is that we goto
>> check_again even when we fail, which should be harmless.
>>
> 
> Really?  If nr_pages gets a value of -EFAULT from the
> __get_user_pages_locked() call, check_and_migrate_cma_pages() will go
> berzerk?

Hmm it should only reach that goto when it migrated something, which
means it won't have to be migrated again, so eventually it should
terminate. But it's very subtle, so I might be wrong.

> And does __get_user_pages_locked() correctly handle a -ve errno
> returned by __get_user_pages()?  It's hard to see how...

I think it does, but agree.

Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-09-04 Thread Vlastimil Babka 
On 9/4/19 8:48 PM, Andrew Morton wrote:
> On Wed, 4 Sep 2019 13:24:58 +0200 Vlastimil Babka  wrote:
> 
>> On 9/4/19 12:26 PM, zhong jiang wrote:
>>> With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
>>> compare with zero. And __get_user_pages_locked will return an long value.
>>> Hence, Convert the long to compare with zero is feasible.
>>
>> It would be nicer if the parameter nr_pages was long again instead of 
>> unsigned
>> long (note there are two variants of the function, so both should be 
>> changed).
> 
> nr_pages should be unsigned - it's a count of pages!

Hm right, I thought check_and_migrate_cma_pages() could be already
called with negative nr_pages from __gup_longterm_locked(), but I missed
there's a if (rc < 0) goto out before that.

> The bug is that __get_user_pages_locked() returns a signed long which
> can be a -ve errno.
> 
> I think it's best if __get_user_pages_locked() is to get itself a new

You mean check_and_migrate_cma_pages()

> local with the same type as its return value.  Something like:

Agreed.

> --- a/mm/gup.c~a
> +++ a/mm/gup.c
> @@ -1450,6 +1450,7 @@ static long check_and_migrate_cma_pages(
>   bool drain_allow = true;
>   bool migrate_allow = true;
>   LIST_HEAD(cma_page_list);
> + long ret;

Should be initialized to nr_pages in case we don't go via "if
(!list_empty(_page_list))" at all.

>  
>  check_again:
>   for (i = 0; i < nr_pages;) {
> @@ -1511,17 +1512,18 @@ check_again:
>* again migrating any new CMA pages which we failed to isolate
>* earlier.
>*/
> - nr_pages = __get_user_pages_locked(tsk, mm, start, nr_pages,
> + ret = __get_user_pages_locked(tsk, mm, start, nr_pages,
>  pages, vmas, NULL,
>  gup_flags);
>  
> - if ((nr_pages > 0) && migrate_allow) {
> + nr_pages = ret;
> + if (ret > 0 && migrate_allow) {
>   drain_allow = true;
>   goto check_again;
>   }
>   }
>  
> - return nr_pages;
> + return ret;
>  }
>  #else
>  static long check_and_migrate_cma_pages(struct task_struct *tsk,
> 
>

Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-09-04 Thread Andrew Morton 
On Wed, 4 Sep 2019 13:24:58 +0200 Vlastimil Babka  wrote:

> On 9/4/19 12:26 PM, zhong jiang wrote:
> > With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
> > compare with zero. And __get_user_pages_locked will return an long value.
> > Hence, Convert the long to compare with zero is feasible.
> 
> It would be nicer if the parameter nr_pages was long again instead of unsigned
> long (note there are two variants of the function, so both should be changed).
> 
> > Signed-off-by: zhong jiang 
> 
> Fixes: 932f4a630a69 ("mm/gup: replace get_user_pages_longterm() with 
> FOLL_LONGTERM")
> 
> (which changed long to unsigned long)
> 
> AFAICS... stable shouldn't be needed as the only "risk" is that we goto
> check_again even when we fail, which should be harmless.
> 

Really?  If nr_pages gets a value of -EFAULT from the
__get_user_pages_locked() call, check_and_migrate_cma_pages() will go
berzerk?

And does __get_user_pages_locked() correctly handle a -ve errno
returned by __get_user_pages()?  It's hard to see how...

Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-09-04 Thread Andrew Morton 
On Wed, 4 Sep 2019 13:24:58 +0200 Vlastimil Babka  wrote:

> On 9/4/19 12:26 PM, zhong jiang wrote:
> > With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
> > compare with zero. And __get_user_pages_locked will return an long value.
> > Hence, Convert the long to compare with zero is feasible.
> 
> It would be nicer if the parameter nr_pages was long again instead of unsigned
> long (note there are two variants of the function, so both should be changed).

nr_pages should be unsigned - it's a count of pages!

The bug is that __get_user_pages_locked() returns a signed long which
can be a -ve errno.

I think it's best if __get_user_pages_locked() is to get itself a new
local with the same type as its return value.  Something like:

--- a/mm/gup.c~a
+++ a/mm/gup.c
@@ -1450,6 +1450,7 @@ static long check_and_migrate_cma_pages(
bool drain_allow = true;
bool migrate_allow = true;
LIST_HEAD(cma_page_list);
+   long ret;
 
 check_again:
for (i = 0; i < nr_pages;) {
@@ -1511,17 +1512,18 @@ check_again:
 * again migrating any new CMA pages which we failed to isolate
 * earlier.
 */
-   nr_pages = __get_user_pages_locked(tsk, mm, start, nr_pages,
+   ret = __get_user_pages_locked(tsk, mm, start, nr_pages,
   pages, vmas, NULL,
   gup_flags);
 
-   if ((nr_pages > 0) && migrate_allow) {
+   nr_pages = ret;
+   if (ret > 0 && migrate_allow) {
drain_allow = true;
goto check_again;
}
}
 
-   return nr_pages;
+   return ret;
 }
 #else
 static long check_and_migrate_cma_pages(struct task_struct *tsk,

Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-09-04 Thread Matthew Wilcox 
On Wed, Sep 04, 2019 at 06:25:19PM +, Weiny, Ira wrote:
> > On 9/4/19 12:26 PM, zhong jiang wrote:
> > > With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
> > > compare with zero. And __get_user_pages_locked will return an long
> > value.
> > > Hence, Convert the long to compare with zero is feasible.
> > 
> > It would be nicer if the parameter nr_pages was long again instead of
> > unsigned long (note there are two variants of the function, so both should 
> > be
> > changed).
> 
> Why?  What does it mean for nr_pages to be negative?  The check below seems 
> valid.  Unsigned can be 0 so the check can fail.  IOW Checking unsigned > 0 
> seems ok.
> 
> What am I missing?

__get_user_pages can return a negative errno.

Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-09-04 Thread Vlastimil Babka 
On 9/4/19 12:26 PM, zhong jiang wrote:
> With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
> compare with zero. And __get_user_pages_locked will return an long value.
> Hence, Convert the long to compare with zero is feasible.

It would be nicer if the parameter nr_pages was long again instead of unsigned
long (note there are two variants of the function, so both should be changed).

> Signed-off-by: zhong jiang 

Fixes: 932f4a630a69 ("mm/gup: replace get_user_pages_longterm() with 
FOLL_LONGTERM")

(which changed long to unsigned long)

AFAICS... stable shouldn't be needed as the only "risk" is that we goto
check_again even when we fail, which should be harmless.

Vlastimil

> ---
>  mm/gup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 23a9f9c..956d5a1 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1508,7 +1508,7 @@ static long check_and_migrate_cma_pages(struct 
> task_struct *tsk,
>  pages, vmas, NULL,
>  gup_flags);
>  
> - if ((nr_pages > 0) && migrate_allow) {
> + if (((long)nr_pages > 0) && migrate_allow) {
>   drain_allow = true;
>   goto check_again;
>   }
>

[PATCH] mm: Unsigned 'nr_pages' always larger than zero

2019-09-04 Thread zhong jiang 
With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
compare with zero. And __get_user_pages_locked will return an long value.
Hence, Convert the long to compare with zero is feasible.

Signed-off-by: zhong jiang 
---
 mm/gup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index 23a9f9c..956d5a1 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1508,7 +1508,7 @@ static long check_and_migrate_cma_pages(struct 
task_struct *tsk,
   pages, vmas, NULL,
   gup_flags);
 
-   if ((nr_pages > 0) && migrate_allow) {
+   if (((long)nr_pages > 0) && migrate_allow) {
drain_allow = true;
goto check_again;
}
-- 
1.7.12.4