linux-kernel - Re: [PATCH 4/4] uprobes: __replace_page() needs munlock_vma

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Message-ID: <20120726051839.GE3810@linux.vnet.ibm.com>
Date:	Thu, 26 Jul 2012 10:48:39 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] uprobes: __replace_page() needs munlock_vma_page()

* Oleg Nesterov <oleg@...hat.com> [2012-07-12 19:10:25]:

> Like do_wp_page(), __replace_page() should do munlock_vma_page()
> for the case when the old page still has other !VM_LOCKED mappings.
> Unfortunately this needs mm/internal.h.
> 
> Also, move put_page() outside of ptl lock. This doesn't really
> matter but looks a bit better.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

One thing I wanted to check is, should we mlock the new page, i.e the
replacing page. It may not a good idea to mlock the new page
because then we can end up adding too many pages to the unevictable
list.

Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

> ---
>  kernel/events/uprobes.c |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index fc1df43..aeea41b 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -32,6 +32,7 @@
>  #include <linux/swap.h>		/* try_to_free_swap */
>  #include <linux/ptrace.h>	/* user_enable_single_step */
>  #include <linux/kdebug.h>	/* notifier mechanism */
> +#include "../../mm/internal.h"	/* munlock_vma_page */
> 
>  #include <linux/uprobes.h>
> 
> @@ -141,7 +142,7 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>  	pte_t *ptep;
>  	int err;
> 
> -	/* freeze PageSwapCache() for try_to_free_swap() below */
> +	/* For try_to_free_swap() and munlock_vma_page() below */
>  	lock_page(page);
> 
>  	err = -EAGAIN;
> @@ -164,9 +165,12 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>  	page_remove_rmap(page);
>  	if (!page_mapped(page))
>  		try_to_free_swap(page);
> -	put_page(page);
>  	pte_unmap_unlock(ptep, ptl);
> 
> +	if (vma->vm_flags & VM_LOCKED)
> +		munlock_vma_page(page);
> +	put_page(page);
> +
>  	err = 0;
>   unlock:
>  	unlock_page(page);
> -- 
> 1.5.5.1
> 

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