linux-kernel - Re: [PATCH 6/7] uprobes: Do not allocate current->utask unnecessary

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Date:	Tue, 8 Jan 2013 17:50:13 +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>,
	Frank Eigler <fche@...hat.com>,
	Josh Stone <jistone@...hat.com>,
	"Suzuki K. Poulose" <suzuki@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] uprobes: Do not allocate current->utask unnecessary

* Oleg Nesterov <oleg@...hat.com> [2012-12-31 18:52:29]:

> handle_swbp() does get_utask() before can_skip_sstep() for no reason,
> we do not need ->utask if can_skip_sstep() succeeds.
> 
> Move get_utask() to pre_ssout() who actually starts to use it. Move
> the initialization of utask->active_uprobe/state as well. This way
> the whole initialization is consolidated in pre_ssout().
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/events/uprobes.c |   16 ++++++----------
>  1 files changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index bd94d2c..ad1245d 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1308,7 +1308,9 @@ pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
>  	unsigned long xol_vaddr;
>  	int err;
> 
> -	utask = current->utask;
> +	utask = get_utask();
> +	if (!utask)
> +		return -ENOMEM;
> 
>  	xol_vaddr = xol_get_insn_slot(uprobe);
>  	if (!xol_vaddr)
> @@ -1323,6 +1325,8 @@ pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
>  		return err;
>  	}
> 
> +	utask->active_uprobe = uprobe;
> +	utask->state = UTASK_SSTEP;
>  	return 0;
>  }
> 
> @@ -1474,7 +1478,6 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
>   */
>  static void handle_swbp(struct pt_regs *regs)
>  {
> -	struct uprobe_task *utask;
>  	struct uprobe *uprobe;
>  	unsigned long bp_vaddr;
>  	int uninitialized_var(is_swbp);
> @@ -1512,19 +1515,12 @@ static void handle_swbp(struct pt_regs *regs)
>  	if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
>  		goto out;
> 
> -	utask = get_utask();
> -	if (!utask)
> -		goto out;	/* re-execute the instruction. */
> -


If get_utask fails with the above change, Dont we end up calling
handler_chain twice(or more)?. I think this is probably true with
previous patch too.

>  	handler_chain(uprobe, regs);
>  	if (can_skip_sstep(uprobe, regs))
>  		goto out;
> 
> -	if (!pre_ssout(uprobe, regs, bp_vaddr)) {
> -		utask->active_uprobe = uprobe;
> -		utask->state = UTASK_SSTEP;
> +	if (!pre_ssout(uprobe, regs, bp_vaddr))
>  		return;
> -	}
> 
>  	/* can_skip_sstep() succeeded, or restart if can't singlestep */
>  out:
> -- 
> 1.5.5.1
> 

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