2018-11-08 17:50:27

by Frank Lee

Subject: [PATCH] mm: mmap: remove verify_mm_writelocked()

We should get rid of this function. It no longer serves its purpose.This
is a historical artifact from 2005 where do_brk was called outside of
the core mm.We do have a proper abstraction in vm_brk_flags and that one
does the locking properly.So there is no need to use this function.

Signed-off-by: Yangtao Li <[email protected]>
---
mm/mmap.c | 16 ----------------
1 file changed, 16 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index f7cd9cb966c0..1cee506494d2 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2910,16 +2910,6 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
return ret;
}

-static inline void verify_mm_writelocked(struct mm_struct *mm)
-{
-#ifdef CONFIG_DEBUG_VM
- if (unlikely(down_read_trylock(&mm->mmap_sem))) {
- WARN_ON(1);
- up_read(&mm->mmap_sem);
- }
-#endif
-}
-
/*
* this is really a simplified "do_mmap". it only handles
* anonymous maps. eventually we may be able to do some
@@ -2946,12 +2936,6 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
if (error)
return error;

- /*
- * mm->mmap_sem is required to protect against another thread
- * changing the mappings in case we sleep.
- */
- verify_mm_writelocked(mm);
-
/*
* Clear old maps. this also does some error checking for us
*/
--
2.17.0

2018-11-08 17:55:20

by Michal Hocko

Subject: Re: [PATCH] mm: mmap: remove verify_mm_writelocked()

On Thu 08-11-18 12:48:56, Yangtao Li wrote:
> We should get rid of this function. It no longer serves its purpose.This
> is a historical artifact from 2005 where do_brk was called outside of
> the core mm.We do have a proper abstraction in vm_brk_flags and that one
> does the locking properly.So there is no need to use this function.
>
> Signed-off-by: Yangtao Li <[email protected]>

Acked-by: Michal Hocko <[email protected]>

> ---
> mm/mmap.c | 16 ----------------
> 1 file changed, 16 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index f7cd9cb966c0..1cee506494d2 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2910,16 +2910,6 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
> return ret;
> }
>
> -static inline void verify_mm_writelocked(struct mm_struct *mm)
> -{
> -#ifdef CONFIG_DEBUG_VM
> - if (unlikely(down_read_trylock(&mm->mmap_sem))) {
> - WARN_ON(1);
> - up_read(&mm->mmap_sem);
> - }
> -#endif
> -}
> -
> /*
> * this is really a simplified "do_mmap". it only handles
> * anonymous maps. eventually we may be able to do some
> @@ -2946,12 +2936,6 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
> if (error)
> return error;
>
> - /*
> - * mm->mmap_sem is required to protect against another thread
> - * changing the mappings in case we sleep.
> - */
> - verify_mm_writelocked(mm);
> -
> /*
> * Clear old maps. this also does some error checking for us
> */
> --
> 2.17.0
>

--
Michal Hocko
SUSE Labs

2018-11-14 22:27:51

by David Rientjes

Subject: Re: [PATCH] mm: mmap: remove verify_mm_writelocked()

On Thu, 8 Nov 2018, Yangtao Li wrote:

> We should get rid of this function. It no longer serves its purpose.This
> is a historical artifact from 2005 where do_brk was called outside of
> the core mm.We do have a proper abstraction in vm_brk_flags and that one
> does the locking properly.So there is no need to use this function.
>
> Signed-off-by: Yangtao Li <[email protected]>

Acked-by: David Rientjes <[email protected]>