Re: [PATCH 7/7] uprobes/perf: Avoid uprobe_apply() whenever possible

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

* Oleg Nesterov <oleg@redhat.com> [2013-02-04 20:03:05]:

> uprobe_perf_open/close call the costly uprobe_apply() every time,
> we can avoid it if:
> 
> 	- "nr_systemwide != 0" is not changed.
> 
> 	- There is another process/thread with the same ->mm.
> 
> 	- copy_proccess() does inherit_event(). dup_mmap() preserves the
> 	  inserted breakpoints.
> 
> 	- event->attr.enable_on_exec == T, we can rely on uprobe_mmap()
> 	  called by exec/mmap paths.
> 
> 	- tp_target is exiting. Only _close() checks PF_EXITING, I don't
> 	  think TRACE_REG_PERF_OPEN can hit the dying task too often.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

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

> ---
>  kernel/trace/trace_uprobe.c |   42 ++++++++++++++++++++++++++++++++++++------
>  1 files changed, 36 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 1114619..e4aab34 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -677,30 +677,60 @@ __uprobe_perf_filter(struct trace_uprobe_filter *filter, struct mm_struct *mm)
>  	return false;
>  }
> 
> +static inline bool
> +uprobe_filter_event(struct trace_uprobe *tu, struct perf_event *event)
> +{
> +	return __uprobe_perf_filter(&tu->filter, event->hw.tp_target->mm);
> +}
> +
>  static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
>  {
> +	bool done;
> +
>  	write_lock(&tu->filter.rwlock);
> -	if (event->hw.tp_target)
> +	if (event->hw.tp_target) {
> +		/*
> +		 * event->parent != NULL means copy_process(), we can avoid
> +		 * uprobe_apply(). current->mm must be probed and we can rely
> +		 * on dup_mmap() which preserves the already installed bp's.
> +		 *
> +		 * attr.enable_on_exec means that exec/mmap will install the
> +		 * breakpoints we need.
> +		 */
> +		done = tu->filter.nr_systemwide ||
> +			event->parent || event->attr.enable_on_exec ||
> +			uprobe_filter_event(tu, event);
>  		list_add(&event->hw.tp_list, &tu->filter.perf_events);
> -	else
> +	} else {
> +		done = tu->filter.nr_systemwide;
>  		tu->filter.nr_systemwide++;
> +	}
>  	write_unlock(&tu->filter.rwlock);
> 
> -	uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
> +	if (!done)
> +		uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
> 
>  	return 0;
>  }
> 
>  static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
>  {
> +	bool done;
> +
>  	write_lock(&tu->filter.rwlock);
> -	if (event->hw.tp_target)
> +	if (event->hw.tp_target) {
>  		list_del(&event->hw.tp_list);
> -	else
> +		done = tu->filter.nr_systemwide ||
> +			(event->hw.tp_target->flags & PF_EXITING) ||
> +			uprobe_filter_event(tu, event);
> +	} else {
>  		tu->filter.nr_systemwide--;
> +		done = tu->filter.nr_systemwide;
> +	}
>  	write_unlock(&tu->filter.rwlock);
> 
> -	uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
> +	if (!done)
> +		uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
> 
>  	return 0;
>  }
> -- 
> 1.5.5.1
> 

-- 
Thanks and Regards
Srikar Dronamraju