linux-kernel - Re: [PATCH 1/1] perf,tools: add time out to force stop endless mmap processing

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Date:	Thu, 11 Jun 2015 11:06:14 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	kan.liang@...el.com
Cc:	linux-kernel@...r.kernel.org, ying.huang@...el.com,
	andi@...stfloor.org
Subject: Re: [PATCH 1/1] perf,tools: add time out to force stop endless mmap
 processing

Em Wed, Jun 10, 2015 at 03:46:04AM -0400, kan.liang@...el.com escreveu:
> perf top reads all threads' /proc/xxx/maps. If there is any threads
> which generating a keeping growing huge /proc/xxx/maps, perf will do
> infinite loop in perf_event__synthesize_mmap_events.
> This patch fixes this issue by adding a time out to force stop this kind
> of endless mmap processing.
> 
> Reported-by: Huang, Ying <ying.huang@...el.com>
> Signed-off-by: Kan Liang <kan.liang@...el.com>

So we will silently stop processing those events?

We will make progress, no doubt, but I think the user needs to be warned
about this situation, so that later on when/if samples for those maps
appear and don't get resolved at least we will know that this is the
reason.

- Arnaldo

> ---
>  tools/perf/util/event.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index 793b150..0df7f2a9 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -213,6 +213,8 @@ static int perf_event__synthesize_fork(struct perf_tool *tool,
>  	return 0;
>  }
>  
> +#define MMAP_TIMEOUT	(50 * 1000000ULL)
> +
>  int perf_event__synthesize_mmap_events(struct perf_tool *tool,
>  				       union perf_event *event,
>  				       pid_t pid, pid_t tgid,
> @@ -222,6 +224,7 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
>  {
>  	char filename[PATH_MAX];
>  	FILE *fp;
> +	unsigned long long t;
>  	int rc = 0;
>  
>  	if (machine__is_default_guest(machine))
> @@ -240,6 +243,7 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
>  	}
>  
>  	event->header.type = PERF_RECORD_MMAP2;
> +	t = rdclock();
>  
>  	while (1) {
>  		char bf[BUFSIZ];
> @@ -250,7 +254,8 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
>  		size_t size;
>  		ssize_t n;
>  
> -		if (fgets(bf, sizeof(bf), fp) == NULL)
> +		if ((fgets(bf, sizeof(bf), fp) == NULL) ||
> +		    ((rdclock() - t) > MMAP_TIMEOUT))
>  			break;
>  
>  		/* ensure null termination since stack will be reused. */
> -- 
> 1.8.3.1
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