[PATCH] mm: vmalloc: don't remove inexistent guard hole in remove_vm_area()

[PATCH] mm: vmalloc: don't remove inexistent guard hole in remove_vm_area()

[Jerome Marchand]

Commit 71394fe50146 ("mm: vmalloc: add flag preventing guard hole
allocation") missed a spot. Currently remove_vm_area() decreases
vm->size to remove the guard hole page, even when it isn't present.
This patch only decreases vm->size when VM_NO_GUARD isn't set.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
---
 mm/vmalloc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d045634..1388c3d 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1443,7 +1443,8 @@ struct vm_struct *remove_vm_area(const void *addr)
 		vmap_debug_free_range(va->va_start, va->va_end);
 		kasan_free_shadow(vm);
 		free_unmap_vmap_area(va);
-		vm->size -= PAGE_SIZE;
+		if (!(vm->flags & VM_NO_GUARD))
+			vm->size -= PAGE_SIZE;
 
 		return vm;
 	}
-- 
2.4.3

Re: [PATCH] mm: vmalloc: don't remove inexistent guard hole in remove_vm_area()

[Andrey Ryabinin]

2015-11-12 18:17 GMT+03:00 Jerome Marchand <jmarchan@redhat.com>:
> Commit 71394fe50146 ("mm: vmalloc: add flag preventing guard hole
> allocation") missed a spot. Currently remove_vm_area() decreases
> vm->size to remove the guard hole page, even when it isn't present.
> This patch only decreases vm->size when VM_NO_GUARD isn't set.
>
> Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
> ---
>  mm/vmalloc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d045634..1388c3d 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1443,7 +1443,8 @@ struct vm_struct *remove_vm_area(const void *addr)
>                 vmap_debug_free_range(va->va_start, va->va_end);
>                 kasan_free_shadow(vm);
>                 free_unmap_vmap_area(va);
> -               vm->size -= PAGE_SIZE;
> +               if (!(vm->flags & VM_NO_GUARD))
> +                       vm->size -= PAGE_SIZE;
>

I'd fix this in another way. I think that remove_vm_area() shouldn't
change vm's size, IMO it doesn't make sense.
The only caller who cares about vm's size after removing is __vunmap():
         area = remove_vm_area(addr);
         ....
         debug_check_no_locks_freed(addr, area->size);
         debug_check_no_obj_freed(addr, area->size);

We already have proper get_vm_area_size() helper which takes
VM_NO_GUARD into account.
So I think we should use that helper for debug_check_no_*() and just
remove 'vm->size -= PAGE_SIZE;' line
from remove_vm_area()



>                 return vm;
>         }
> --
> 2.4.3
>

Re: [PATCH] mm: vmalloc: don't remove inexistent guard hole in remove_vm_area()

[Jerome Marchand]

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On 11/12/2015 04:55 PM, Andrey Ryabinin wrote:
> 2015-11-12 18:17 GMT+03:00 Jerome Marchand <jmarchan@redhat.com>:
>> Commit 71394fe50146 ("mm: vmalloc: add flag preventing guard hole
>> allocation") missed a spot. Currently remove_vm_area() decreases
>> vm->size to remove the guard hole page, even when it isn't present.
>> This patch only decreases vm->size when VM_NO_GUARD isn't set.
>>
>> Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
>> ---
>>  mm/vmalloc.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index d045634..1388c3d 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -1443,7 +1443,8 @@ struct vm_struct *remove_vm_area(const void *addr)
>>                 vmap_debug_free_range(va->va_start, va->va_end);
>>                 kasan_free_shadow(vm);
>>                 free_unmap_vmap_area(va);
>> -               vm->size -= PAGE_SIZE;
>> +               if (!(vm->flags & VM_NO_GUARD))
>> +                       vm->size -= PAGE_SIZE;
>>
> 
> I'd fix this in another way. I think that remove_vm_area() shouldn't
> change vm's size, IMO it doesn't make sense.
> The only caller who cares about vm's size after removing is __vunmap():
>          area = remove_vm_area(addr);
>          ....
>          debug_check_no_locks_freed(addr, area->size);
>          debug_check_no_obj_freed(addr, area->size);
> 
> We already have proper get_vm_area_size() helper which takes
> VM_NO_GUARD into account.
> So I think we should use that helper for debug_check_no_*() and just
> remove 'vm->size -= PAGE_SIZE;' line
> from remove_vm_area()

Sure, that would be cleaner.

Btw, there might be a leak in sq_unmap() (arch/sh/kernel/cpu/sh4/sq.c)
as the vm_struct doesn't seem to be freed. CCed the SuperH folks.

Thanks,
Jerome

> 
> 
> 
>>                 return vm;
>>         }
>> --
>> 2.4.3
>>



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[PATCH V2] mm: vmalloc: don't remove inexistent guard hole in remove_vm_area()

[Jerome Marchand]

Commit 71394fe50146 ("mm: vmalloc: add flag preventing guard hole
allocation") missed a spot. Currently remove_vm_area() decreases
vm->size to "remove" the guard hole page, even when it isn't present.
All but one users just free the vm_struct rigth away and never access
vm->size anyway.
Don't touch the size in remove_vm_area() and have __vunmap() use the
proper get_vm_area_size() helper.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
---
 mm/vmalloc.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d045634..8e3c9c5 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1443,7 +1443,6 @@ struct vm_struct *remove_vm_area(const void *addr)
 		vmap_debug_free_range(va->va_start, va->va_end);
 		kasan_free_shadow(vm);
 		free_unmap_vmap_area(va);
-		vm->size -= PAGE_SIZE;
 
 		return vm;
 	}
@@ -1468,8 +1467,8 @@ static void __vunmap(const void *addr, int deallocate_pages)
 		return;
 	}
 
-	debug_check_no_locks_freed(addr, area->size);
-	debug_check_no_obj_freed(addr, area->size);
+	debug_check_no_locks_freed(addr, get_vm_area_size(area));
+	debug_check_no_obj_freed(addr, get_vm_area_size(area));
 
 	if (deallocate_pages) {
 		int i;
-- 
2.4.3

Re: [PATCH V2] mm: vmalloc: don't remove inexistent guard hole in remove_vm_area()

[Andrey Ryabinin]

2015-11-12 19:37 GMT+03:00 Jerome Marchand <jmarchan@redhat.com>:
> Commit 71394fe50146 ("mm: vmalloc: add flag preventing guard hole
> allocation") missed a spot. Currently remove_vm_area() decreases
> vm->size to "remove" the guard hole page, even when it isn't present.
> All but one users just free the vm_struct rigth away and never access
> vm->size anyway.
> Don't touch the size in remove_vm_area() and have __vunmap() use the
> proper get_vm_area_size() helper.
>
> Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

Re: [PATCH V2] mm: vmalloc: don't remove inexistent guard hole in remove_vm_area()

[David Rientjes]

On Thu, 12 Nov 2015, Jerome Marchand wrote:

> Commit 71394fe50146 ("mm: vmalloc: add flag preventing guard hole
> allocation") missed a spot. Currently remove_vm_area() decreases
> vm->size to "remove" the guard hole page, even when it isn't present.
> All but one users just free the vm_struct rigth away and never access
> vm->size anyway.
> Don't touch the size in remove_vm_area() and have __vunmap() use the
> proper get_vm_area_size() helper.
> 
> Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

Acked-by: David Rientjes <rientjes@google.com>