Re: [PATCH] mm: mmap: remove unnecessary unlikely()

[Michal Hocko]

On Sun 04-11-18 07:44:56, Yangtao Li wrote:
> WARN_ON() already contains an unlikely(), so it's not necessary to use
> unlikely.

We should just get rid of this ugliness altogether. 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.

> 
> Signed-off-by: Yangtao Li 
> ---
>  mm/mmap.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 6c04292e16a7..2077008ade0c 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2965,10 +2965,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, 
> start, unsigned long, size,
>  static inline void verify_mm_writelocked(struct mm_struct *mm)
>  {
>  #ifdef CONFIG_DEBUG_VM
> - if (unlikely(down_read_trylock(>mmap_sem))) {
> - WARN_ON(1);
> + if (WARN_ON(down_read_trylock(>mmap_sem)))
>   up_read(>mmap_sem);
> - }
>  #endif
>  }
>  
> -- 
> 2.17.0
> 

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] mm: mmap: remove unnecessary unlikely()

[Michal Hocko]

On Sun 04-11-18 07:44:56, Yangtao Li wrote:
> WARN_ON() already contains an unlikely(), so it's not necessary to use
> unlikely.

We should just get rid of this ugliness altogether. 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.

> 
> Signed-off-by: Yangtao Li 
> ---
>  mm/mmap.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 6c04292e16a7..2077008ade0c 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2965,10 +2965,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, 
> start, unsigned long, size,
>  static inline void verify_mm_writelocked(struct mm_struct *mm)
>  {
>  #ifdef CONFIG_DEBUG_VM
> - if (unlikely(down_read_trylock(>mmap_sem))) {
> - WARN_ON(1);
> + if (WARN_ON(down_read_trylock(>mmap_sem)))
>   up_read(>mmap_sem);
> - }
>  #endif
>  }
>  
> -- 
> 2.17.0
> 

-- 
Michal Hocko
SUSE Labs

[PATCH] mm: mmap: remove unnecessary unlikely()

[Yangtao Li]

WARN_ON() already contains an unlikely(), so it's not necessary to use
unlikely.

Signed-off-by: Yangtao Li 
---
 mm/mmap.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 6c04292e16a7..2077008ade0c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2965,10 +2965,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, 
unsigned long, size,
 static inline void verify_mm_writelocked(struct mm_struct *mm)
 {
 #ifdef CONFIG_DEBUG_VM
-   if (unlikely(down_read_trylock(>mmap_sem))) {
-   WARN_ON(1);
+   if (WARN_ON(down_read_trylock(>mmap_sem)))
up_read(>mmap_sem);
-   }
 #endif
 }
 
-- 
2.17.0

[PATCH] mm: mmap: remove unnecessary unlikely()

[Yangtao Li]

WARN_ON() already contains an unlikely(), so it's not necessary to use
unlikely.

Signed-off-by: Yangtao Li 
---
 mm/mmap.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 6c04292e16a7..2077008ade0c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2965,10 +2965,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, 
unsigned long, size,
 static inline void verify_mm_writelocked(struct mm_struct *mm)
 {
 #ifdef CONFIG_DEBUG_VM
-   if (unlikely(down_read_trylock(>mmap_sem))) {
-   WARN_ON(1);
+   if (WARN_ON(down_read_trylock(>mmap_sem)))
up_read(>mmap_sem);
-   }
 #endif
 }
 
-- 
2.17.0