linux-kernel - Re: [PATCH 1/3] uprobes: Kill uprobe_events, use RB_EMPTY

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Message-ID: <20121213143501.GF3902@linux.vnet.ibm.com>
Date:	Thu, 13 Dec 2012 20:05:01 +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>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] uprobes: Kill uprobe_events, use RB_EMPTY_ROOT()
 instead

* Oleg Nesterov <oleg@...hat.com> [2012-11-25 23:33:44]:

> uprobe_events counts the number of uprobes in uprobes_tree but
> it is used as a boolean. We can use RB_EMPTY_ROOT() instead.
> 

Nice idea.

> Probably no_uprobe_events() added by this patch can have more
> callers, say, mmf_recalc_uprobes().
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---

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

>  kernel/events/uprobes.c |   19 +++++++------------
>  1 files changed, 7 insertions(+), 12 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 1e047f8..53dc2eb 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -41,6 +41,11 @@
>  #define MAX_UPROBE_XOL_SLOTS		UINSNS_PER_PAGE
> 
>  static struct rb_root uprobes_tree = RB_ROOT;
> +/*
> + * allows us to skip the uprobe_mmap if there are no uprobe events active
> + * at this time.  Probably a fine grained per inode count is better?
> + */
> +#define no_uprobe_events()	RB_EMPTY_ROOT(&uprobes_tree)
> 
>  static DEFINE_SPINLOCK(uprobes_treelock);	/* serialize rbtree access */
> 
> @@ -74,13 +79,6 @@ static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ];
> 
>  static struct percpu_rw_semaphore dup_mmap_sem;
> 
> -/*
> - * uprobe_events allows us to skip the uprobe_mmap if there are no uprobe
> - * events active at this time.  Probably a fine grained per inode count is
> - * better?
> - */
> -static atomic_t uprobe_events = ATOMIC_INIT(0);
> -
>  /* Have a copy of original instruction */
>  #define UPROBE_COPY_INSN	0
>  /* Can skip singlestep */
> @@ -460,8 +458,6 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
>  		kfree(uprobe);
>  		uprobe = cur_uprobe;
>  		iput(inode);
> -	} else {
> -		atomic_inc(&uprobe_events);
>  	}
> 
>  	return uprobe;
> @@ -685,7 +681,6 @@ static void delete_uprobe(struct uprobe *uprobe)
>  	spin_unlock(&uprobes_treelock);
>  	iput(uprobe->inode);
>  	put_uprobe(uprobe);
> -	atomic_dec(&uprobe_events);
>  }
> 
>  struct map_info {
> @@ -975,7 +970,7 @@ int uprobe_mmap(struct vm_area_struct *vma)
>  	struct uprobe *uprobe, *u;
>  	struct inode *inode;
> 
> -	if (!atomic_read(&uprobe_events) || !valid_vma(vma, true))
> +	if (no_uprobe_events() || !valid_vma(vma, true))
>  		return 0;
> 
>  	inode = vma->vm_file->f_mapping->host;
> @@ -1021,7 +1016,7 @@ vma_has_uprobes(struct vm_area_struct *vma, unsigned long start, unsigned long e
>   */
>  void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end)
>  {
> -	if (!atomic_read(&uprobe_events) || !valid_vma(vma, false))
> +	if (no_uprobe_events() || !valid_vma(vma, false))
>  		return;
> 
>  	if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */
> -- 
> 1.5.5.1
> 

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