Messages in this thread | | | Date | Wed, 22 Mar 2023 12:59:28 +0200 | Subject | Re: [PATCH] perf/core: Fix the same task check in perf_event_set_output | From | Adrian Hunter <> |
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On 11/07/22 21:07, kan.liang@linux.intel.com wrote: > 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>
Did this slip through the cracks, or is there more complexity to this case than just sharing the rb?
> --- > 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; > > /*
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