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

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Date:	Wed, 23 Oct 2013 11:46:05 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Davidlohr Bueso <davidlohr@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Michel Lespinasse <walken@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>, aswin@...com,
	linux-mm <linux-mm@...ck.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm/mlock: prepare params outside critical region

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 <davidlohr@...com>
> Cc: Michel Lespinasse <walken@...gle.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>

Acked-by: Vlastimil Babka <vbabka@...e.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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