Re: [PATCH 2/3] mm/mlock: prepare params outside critical region

[Vlastimil Babka]

On 10/18/2013 02:50 AM, Davidlohr Bueso wrote:
> All mlock related syscalls prepare lock limits, lengths and
> start parameters with the mmap_sem held. Move this logic
> outside of the critical region. For the case of mlock, continue
> incrementing the amount already locked by mm->locked_vm with
> the rwsem taken.
> 
> Signed-off-by: Davidlohr Bueso <davidl...@hp.com>
> Cc: Michel Lespinasse <wal...@google.com>
> Cc: Vlastimil Babka <vba...@suse.cz>

Acked-by: Vlastimil Babka <vba...@suse.cz>

> ---
>  mm/mlock.c | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/mlock.c b/mm/mlock.c
> index d480cd6..aa7de13 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -689,19 +689,21 @@ SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, 
> len)
>  
>       lru_add_drain_all();    /* flush pagevec */
>  
> -     down_write(&current->mm->mmap_sem);
>       len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
>       start &= PAGE_MASK;
>  
> -     locked = len >> PAGE_SHIFT;
> -     locked += current->mm->locked_vm;
> -
>       lock_limit = rlimit(RLIMIT_MEMLOCK);
>       lock_limit >>= PAGE_SHIFT;
> +     locked = len >> PAGE_SHIFT;
> +
> +     down_write(&current->mm->mmap_sem);
> +
> +     locked += current->mm->locked_vm;
>  
>       /* check against resource limits */
>       if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
>               error = do_mlock(start, len, 1);
> +
>       up_write(&current->mm->mmap_sem);
>       if (!error)
>               error = __mm_populate(start, len, 0);
> @@ -712,11 +714,13 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, 
> len)
>  {
>       int ret;
>  
> -     down_write(&current->mm->mmap_sem);
>       len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
>       start &= PAGE_MASK;
> +
> +     down_write(&current->mm->mmap_sem);
>       ret = do_mlock(start, len, 0);
>       up_write(&current->mm->mmap_sem);
> +
>       return ret;
>  }
>  
> @@ -761,12 +765,12 @@ SYSCALL_DEFINE1(mlockall, int, flags)
>       if (flags & MCL_CURRENT)
>               lru_add_drain_all();    /* flush pagevec */
>  
> -     down_write(&current->mm->mmap_sem);
> -
>       lock_limit = rlimit(RLIMIT_MEMLOCK);
>       lock_limit >>= PAGE_SHIFT;
>  
>       ret = -ENOMEM;
> +     down_write(&current->mm->mmap_sem);
> +
>       if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
>           capable(CAP_IPC_LOCK))
>               ret = do_mlockall(flags);
> 

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