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 14:27:40 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	"andi@...stfloor.org" <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.
> 

I will add warning message for this kind of time out.

Thanks,
Kan

> - 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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