Re: [PATCH 3/4] uprobes: Kill UPROBE_RUN_HANDLER flag

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

* Oleg Nesterov <oleg@redhat.com> [2012-11-24 19:02:33]:

> Simply remove UPROBE_RUN_HANDLER and the corresponding code.
> 
> It can only help if uprobe has a single consumer, and in fact
> it is no longer needed after handler_chain() was changed to use
> ->register_rwsem, we simply can not race with uprobe_register().
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>


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

> ---
>  kernel/events/uprobes.c |   23 +++++------------------
>  1 files changed, 5 insertions(+), 18 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 873c993..97c3874 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -83,10 +83,8 @@ static atomic_t uprobe_events = ATOMIC_INIT(0);
> 
>  /* Have a copy of original instruction */
>  #define UPROBE_COPY_INSN	0
> -/* Dont run handlers when first register/ last unregister in progress*/
> -#define UPROBE_RUN_HANDLER	1
>  /* Can skip singlestep */
> -#define UPROBE_SKIP_SSTEP	2
> +#define UPROBE_SKIP_SSTEP	1
> 
>  struct uprobe {
>  	struct rb_node		rb_node;	/* node in the rb tree */
> @@ -475,9 +473,6 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
>  {
>  	struct uprobe_consumer *uc;
> 
> -	if (!test_bit(UPROBE_RUN_HANDLER, &uprobe->flags))
> -		return;
> -
>  	down_read(&uprobe->register_rwsem);
>  	for (uc = uprobe->consumers; uc; uc = uc->next)
>  		uc->handler(uc, regs);
> @@ -825,13 +820,8 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
> 
>  static int __uprobe_register(struct uprobe *uprobe, struct uprobe_consumer *uc)
>  {
> -	int err;
> -
>  	consumer_add(uprobe, uc);
> -	err = register_for_each_vma(uprobe, true);
> -	if (!err) /* TODO: pointless unless the first consumer */
> -		set_bit(UPROBE_RUN_HANDLER, &uprobe->flags);
> -	return err;
> +	return register_for_each_vma(uprobe, true);
>  }
> 
>  static void __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
> @@ -842,12 +832,9 @@ static void __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *u
>  		return;
> 
>  	err = register_for_each_vma(uprobe, false);
> -	if (!uprobe->consumers) {
> -		clear_bit(UPROBE_RUN_HANDLER, &uprobe->flags);
> -		/* TODO : cant unregister? schedule a worker thread */
> -		if (!err)
> -			delete_uprobe(uprobe);
> -	}
> +	/* TODO : cant unregister? schedule a worker thread */
> +	if (!uprobe->consumers && !err)
> +		delete_uprobe(uprobe);
>  }
> 
>  /*
> -- 
> 1.5.5.1
>