Re: [PATCH 2/3] uprobes: Introduce uprobe_is_active()

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Oleg Nesterov <oleg@redhat.com> [2012-11-25 23:33:47]:

> The lifetime of uprobe->rb_node and uprobe->inode is not refcounted,
> delete_uprobe() is called when we detect that uprobe has no consumers,
> and it would be deadly wrong to do this twice.
> 
> Change delete_uprobe() to WARN() if it was already called. We use
> RB_CLEAR_NODE() to mark uprobe "inactive", then RB_EMPTY_NODE() can
> be used to detect this case.
> 
> RB_EMPTY_NODE() is not used directly, we add the trivial helper for
> the next change.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

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

> ---
>  kernel/events/uprobes.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 53dc2eb..2886c82 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -669,6 +669,10 @@ remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vad
>  	return set_orig_insn(&uprobe->arch, mm, vaddr);
>  }
> 
> +static inline bool uprobe_is_active(struct uprobe *uprobe)
> +{
> +	return !RB_EMPTY_NODE(&uprobe->rb_node);
> +}
>  /*
>   * There could be threads that have already hit the breakpoint. They
>   * will recheck the current insn and restart if find_uprobe() fails.
> @@ -676,9 +680,13 @@ remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vad
>   */
>  static void delete_uprobe(struct uprobe *uprobe)
>  {
> +	if (WARN_ON(!uprobe_is_active(uprobe)))
> +		return;
> +
>  	spin_lock(&uprobes_treelock);
>  	rb_erase(&uprobe->rb_node, &uprobes_tree);
>  	spin_unlock(&uprobes_treelock);
> +	RB_CLEAR_NODE(&uprobe->rb_node); /* for uprobe_is_active() */
>  	iput(uprobe->inode);
>  	put_uprobe(uprobe);
>  }
> -- 
> 1.5.5.1
>