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perf tools: Don't clone maps from parent when synthesizing forks

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When synthesizing FORK events, we are trying to create thread objects
for the already running tasks on the machine.

Normally, for a kernel FORK event, we want to clone the parent's maps
because that is what the kernel just did.

But when synthesizing, this should not be done.  If we do, we end up
with overlapping maps as we process the sythesized MMAP2 events that
get delivered shortly thereafter.

Use the FORK event misc flags in an internal way to signal this
situation, so we can elide the map clone when appropriate.

Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Joe Mario <jmario@redhat.com>
Link: http://lkml.kernel.org/r/20181030.222404.2085088822877051075.davem@davemloft.net
[ Added comment about flag use in machine__process_fork_event(),
  use ternary op in thread__clone_map_groups() as suggested by Jiri ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
David Miller 2018-10-30 22:24:04 -07:00 • committed by Arnaldo Carvalho de Melo
parent ff27a06af6
commit 4f8f382e63
6 changed files with 29 additions and 10 deletions
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19
tools/perf/util/machine.c
View file

@ -1708,6 +1708,7 @@ int machine__process_fork_event(struct machine *machine, union perf_event *event
struct thread *parent = machine__findnew_thread(machine,
event->fork.ppid,
event->fork.ptid);
bool do_maps_clone = true;
int err = 0;
if (dump_trace)
@ -1736,9 +1737,25 @@ int machine__process_fork_event(struct machine *machine, union perf_event *event
thread = machine__findnew_thread(machine, event->fork.pid,
event->fork.tid);
/*
* When synthesizing FORK events, we are trying to create thread
* objects for the already running tasks on the machine.
*
* Normally, for a kernel FORK event, we want to clone the parent's
* maps because that is what the kernel just did.
*
* But when synthesizing, this should not be done. If we do, we end up
* with overlapping maps as we process the sythesized MMAP2 events that
* get delivered shortly thereafter.
*
* Use the FORK event misc flags in an internal way to signal this
* situation, so we can elide the map clone when appropriate.
*/
if (event->fork.header.misc & PERF_RECORD_MISC_FORK_EXEC)
do_maps_clone = false;
if (thread == NULL || parent == NULL ||
thread__fork(thread, parent, sample->time) < 0) {
thread__fork(thread, parent, sample->time, do_maps_clone) < 0) {
dump_printf("problem processing PERF_RECORD_FORK, skipping event.\n");
err = -1;
}