linux-kernel - Re: [PATCH] uprobes: Add uprobe_task->dup_work/dup

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Date:	Mon, 11 Nov 2013 10:43:58 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uprobes: Add uprobe_task->dup_work/dup_addr

(2013/11/09 4:00), Oleg Nesterov wrote:
> uprobe_task->vaddr is a bit strange. First of all it is not really
> needed, we can move it into arch_uprobe_task. The generic code uses
> it only to pass the additional argument to arch_uprobe_pre_xol(),
> and since it is always equal to instruction_pointer() this looks
> even more strange.
> 
> And both utask->vaddr and and utask->autask have the same scope,
> they only have the meaning when the task executes the probed insn
> out-of-line. This means it is safe to reuse both in UTASK_RUNNING
> state.
> 
> OTOH, it is also used by uprobe_copy_process() and dup_xol_work()
> for another purpose, this doesn't look clean and doesn't allow to
> move this member into arch_uprobe_task.
> 
> This patch adds the union with 2 anonymous structs into uprobe_task.
> 
> The first struct is autask + vaddr, this way we "almost" move vaddr
> into autask.
> 
> The second struct has 2 new members for uprobe_copy_process() paths:
> ->dup_addr which can be used instead ->vaddr, and ->dup_work which
> can be used to avoid kmalloc() and simplify the code.
> 
> Note that this union will likely have another member(s), we need
> something like "private_data_for_handlers" so that the tracing
> handlers could use it to communicate with call_fetch() methods.

OK, those are used in the different phase as a scratchpad.

> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Thanks!

> ---
>  include/linux/uprobes.h |   21 ++++++++++++++++-----
>  kernel/events/uprobes.c |   16 ++++------------
>  2 files changed, 20 insertions(+), 17 deletions(-)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 319eae7..366b8b2 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -26,6 +26,7 @@
>  
>  #include <linux/errno.h>
>  #include <linux/rbtree.h>
> +#include <linux/types.h>
>  
>  struct vm_area_struct;
>  struct mm_struct;
> @@ -72,14 +73,24 @@ enum uprobe_task_state {
>   */
>  struct uprobe_task {
>  	enum uprobe_task_state		state;
> -	struct arch_uprobe_task		autask;
>  
> -	struct return_instance		*return_instances;
> -	unsigned int			depth;
> -	struct uprobe			*active_uprobe;
> +	union {
> +		struct {
> +			struct arch_uprobe_task	autask;
> +			unsigned long		vaddr;
> +		};
> +
> +		struct {
> +			struct callback_head	dup_work;
> +			unsigned long		dup_addr;
> +		};
> +	};
>  
> +	struct uprobe			*active_uprobe;
>  	unsigned long			xol_vaddr;
> -	unsigned long			vaddr;
> +
> +	struct return_instance		*return_instances;
> +	unsigned int			depth;
>  };
>  
>  /*
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 24b7d6c..2546a7b 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1403,12 +1403,10 @@ static void uprobe_warn(struct task_struct *t, const char *msg)
>  
>  static void dup_xol_work(struct callback_head *work)
>  {
> -	kfree(work);
> -
>  	if (current->flags & PF_EXITING)
>  		return;
>  
> -	if (!__create_xol_area(current->utask->vaddr))
> +	if (!__create_xol_area(current->utask->dup_addr))
>  		uprobe_warn(current, "dup xol area");
>  }
>  
> @@ -1419,7 +1417,6 @@ void uprobe_copy_process(struct task_struct *t, unsigned long flags)
>  {
>  	struct uprobe_task *utask = current->utask;
>  	struct mm_struct *mm = current->mm;
> -	struct callback_head *work;
>  	struct xol_area *area;
>  
>  	t->utask = NULL;
> @@ -1441,14 +1438,9 @@ void uprobe_copy_process(struct task_struct *t, unsigned long flags)
>  	if (mm == t->mm)
>  		return;
>  
> -	/* TODO: move it into the union in uprobe_task */
> -	work = kmalloc(sizeof(*work), GFP_KERNEL);
> -	if (!work)
> -		return uprobe_warn(t, "dup xol area");
> -
> -	t->utask->vaddr = area->vaddr;
> -	init_task_work(work, dup_xol_work);
> -	task_work_add(t, work, true);
> +	t->utask->dup_addr = area->vaddr;
> +	init_task_work(&t->utask->dup_work, dup_xol_work);
> +	task_work_add(t, &t->utask->dup_work, true);
>  }
>  
>  /*
> 


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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