linux-kernel - Re: [PATCH 4/5] uprobes: Kill UTASK_BP

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Date:	Thu, 20 Sep 2012 19:36:09 +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>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] uprobes: Kill UTASK_BP_HIT state

* Oleg Nesterov <oleg@...hat.com> [2012-09-14 19:16:00]:

> Kill UTASK_BP_HIT state, it buys nothing but complicates the code.
> It is only used in uprobe_notify_resume() to decide who should be
> called, we can check utask->active_uprobe != NULL instead. And this
> allows us to simplify handle_swbp(), no need to clear utask->state.
> 
> Likewise we could kill UTASK_SSTEP, but UTASK_BP_HIT is worse and
> imho should die. The problem is, it creates the special case when
> task->utask is NULL, we can't distinguish RUNNING and BP_HIT. With
> his patch utask == NULL always means RUNNING.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>


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

> ---
>  include/linux/uprobes.h |    1 -
>  kernel/events/uprobes.c |   29 +++++++++--------------------
>  2 files changed, 9 insertions(+), 21 deletions(-)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index e6f0331..18d839d 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -59,7 +59,6 @@ struct uprobe_consumer {
>  #ifdef CONFIG_UPROBES
>  enum uprobe_task_state {
>  	UTASK_RUNNING,
> -	UTASK_BP_HIT,
>  	UTASK_SSTEP,
>  	UTASK_SSTEP_ACK,
>  	UTASK_SSTEP_TRAPPED,
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 403d2e0..4ea0f0b 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1469,10 +1469,6 @@ static void handle_swbp(struct pt_regs *regs)
>  	bp_vaddr = uprobe_get_swbp_addr(regs);
>  	uprobe = find_active_uprobe(bp_vaddr, &is_swbp);
> 
> -	utask = current->utask;
> -	if (utask)
> -		utask->state = UTASK_RUNNING;
> -
>  	if (!uprobe) {
>  		if (is_swbp > 0) {
>  			/* No matching uprobe; signal SIGTRAP. */
> @@ -1491,6 +1487,7 @@ static void handle_swbp(struct pt_regs *regs)
>  		return;
>  	}
> 
> +	utask = current->utask;
>  	if (!utask) {
>  		utask = add_utask();
>  		/* Cannot allocate; re-execute the instruction. */
> @@ -1547,13 +1544,12 @@ static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
>  }
> 
>  /*
> - * On breakpoint hit, breakpoint notifier sets the TIF_UPROBE flag.  (and on
> - * subsequent probe hits on the thread sets the state to UTASK_BP_HIT) and
> - * allows the thread to return from interrupt.
> + * On breakpoint hit, breakpoint notifier sets the TIF_UPROBE flag and
> + * allows the thread to return from interrupt. After that handle_swbp()
> + * sets utask->active_uprobe.
>   *
> - * On singlestep exception, singlestep notifier sets the TIF_UPROBE flag and
> - * also sets the state to UTASK_SSTEP_ACK and allows the thread to return from
> - * interrupt.
> + * On singlestep exception, singlestep notifier sets the TIF_UPROBE flag
> + * and allows the thread to return from interrupt.
>   *
>   * While returning to userspace, thread notices the TIF_UPROBE flag and calls
>   * uprobe_notify_resume().
> @@ -1563,10 +1559,10 @@ void uprobe_notify_resume(struct pt_regs *regs)
>  	struct uprobe_task *utask;
> 
>  	utask = current->utask;
> -	if (!utask || utask->state == UTASK_BP_HIT)
> -		handle_swbp(regs);
> -	else
> +	if (utask && utask->active_uprobe)
>  		handle_singlestep(utask, regs);
> +	else
> +		handle_swbp(regs);
>  }
> 
>  /*
> @@ -1575,17 +1571,10 @@ void uprobe_notify_resume(struct pt_regs *regs)
>   */
>  int uprobe_pre_sstep_notifier(struct pt_regs *regs)
>  {
> -	struct uprobe_task *utask;
> -
>  	if (!current->mm || !test_bit(MMF_HAS_UPROBES, &current->mm->flags))
>  		return 0;
> 
> -	utask = current->utask;
> -	if (utask)
> -		utask->state = UTASK_BP_HIT;
> -
>  	set_thread_flag(TIF_UPROBE);
> -
>  	return 1;
>  }
> 
> -- 
> 1.5.5.1
> 

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