Messages in this thread Patch in this message | | | From | kan.liang@linux ... | Subject | [PATCH] perf/core: Fix the same task check in perf_event_set_output | Date | Mon, 11 Jul 2022 11:07:06 -0700 |
| |
From: Kan Liang <kan.liang@linux.intel.com>
With the --per-thread option, perf record errors out when sampling with a hardware event and a software event as below.
$ perf record -e cycles,dummy --per-thread ls failed to mmap with 22 (Invalid argument)
The same task is sampled with the two events. The IOC_OUTPUT is invoked to share the mmap memory of the task between the events. In the perf_event_set_output(), the event->ctx is used to check whether the two events are attached to the same task. However, a hardware event and a software event are from different task context. The check always fails.
The task struct is stored in the event->hw.target for each per-thread event. It can be used to determine whether two events are attached to the same task.
The patch can also fix another issue reported months ago. https://lore.kernel.org/all/92645262-D319-4068-9C44-2409EF44888E@gmail.com/ The event->ctx is not ready when the perf_event_set_output() is invoked in the perf_event_open(), while the event->hw.target has been assigned at the moment.
The problem should be a long time issue since commit c3f00c70276d ("perf: Separate find_get_context() from event initialization"). The event->hw.target doesn't exist at that time. Here, the patch which introduces the event->hw.target is used by the Fixes tag.
The problem should still exists between the broken patch and the event->hw.target patch. This patch does not intend to fix that case.
Fixes: 50f16a8bf9d7 ("perf: Remove type specific target pointers") Reviewed-by: Zhengjun Xing <zhengjun.xing@linux.intel.com> Signed-off-by: Kan Liang <kan.liang@linux.intel.com> --- kernel/events/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index b4d62210c3e5..22df79d3f19d 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -12080,7 +12080,7 @@ perf_event_set_output(struct perf_event *event, struct perf_event *output_event) /* * If its not a per-cpu rb, it must be the same task. */ - if (output_event->cpu == -1 && output_event->ctx != event->ctx) + if (output_event->cpu == -1 && output_event->hw.target != event->hw.target) goto out; /* -- 2.35.1
| |