* [PATCH] mm: mmap: remove unnecessary unlikely()
@ 2018-11-04 12:44 Yangtao Li
2018-11-05 6:51 ` Michal Hocko
0 siblings, 1 reply; 2+ messages in thread
From: Yangtao Li @ 2018-11-04 12:44 UTC (permalink / raw)
To: akpm, mhocko, kirill.shutemov, vbabka, yang.shi, rientjes, linux
Cc: linux-mm, linux-kernel, Yangtao Li
WARN_ON() already contains an unlikely(), so it's not necessary to use
unlikely.
Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
---
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(&mm->mmap_sem))) {
- WARN_ON(1);
+ if (WARN_ON(down_read_trylock(&mm->mmap_sem)))
up_read(&mm->mmap_sem);
- }
#endif
}
--
2.17.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] mm: mmap: remove unnecessary unlikely()
2018-11-04 12:44 [PATCH] mm: mmap: remove unnecessary unlikely() Yangtao Li
@ 2018-11-05 6:51 ` Michal Hocko
0 siblings, 0 replies; 2+ messages in thread
From: Michal Hocko @ 2018-11-05 6:51 UTC (permalink / raw)
To: Yangtao Li
Cc: akpm, kirill.shutemov, vbabka, yang.shi, rientjes, linux,
linux-mm, linux-kernel
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 <tiny.windzz@gmail.com>
> ---
> 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(&mm->mmap_sem))) {
> - WARN_ON(1);
> + if (WARN_ON(down_read_trylock(&mm->mmap_sem)))
> up_read(&mm->mmap_sem);
> - }
> #endif
> }
>
> --
> 2.17.0
>
--
Michal Hocko
SUSE Labs
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