Messages in this thread | | | Subject | Re: [PATCH v3 05/13] coresight: perf: Allow tracing on hotplugged CPUs | From | Suzuki K Poulose <> | Date | Wed, 1 Aug 2018 00:08:12 +0100 |
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On 07/31/2018 06:46 PM, Mathieu Poirier wrote: > On Thu, Jul 26, 2018 at 01:54:43PM +0100, Suzuki K Poulose wrote: >> At the moment, if there is no CPU specified for a given >> event, we use cpu_online_mask and try to build path for >> each of the CPUs in the mask. This could prevent any CPU >> that is turned online later to be used for the tracing. >> >> This patch changes to use the cpu_present_mask and tries >> to build path for as much CPUs as possible ignoring the >> failures in building path for some of the CPUs. If ever >> we try to trace on those CPUs, we fail the operation. >> >> Based on a patch from Mathieu Poirier. >> >> Cc: Mathieu Poirier <mathieu.poirier@linaro.org> >> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >> --- >> drivers/hwtracing/coresight/coresight-etm-perf.c | 46 +++++++++++++++--------- >> 1 file changed, 30 insertions(+), 16 deletions(-) >> >> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c >> index 6beb662..afe7e7f 100644 >> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c >> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c >> @@ -127,11 +127,9 @@ static void free_event_data(struct work_struct *work) >> >> event_data = container_of(work, struct etm_event_data, work); >> mask = &event_data->mask; >> - /* >> - * First deal with the sink configuration. See comment in >> - * etm_setup_aux() about why we take the first available path. >> - */ >> - if (event_data->snk_config) { >> + >> + /* Free the sink buffers, if there are any */ >> + if (event_data->snk_config && !WARN_ON(cpumask_empty(mask))) { > > I'm not sure the WARN_ON() is required. > > Here @mask can't be empty since you've added a check in setup_aux(). So if > @mask does end up being empty something has trampled the memory and we have > far bigger problems.
And thats exactly why I have a WARN_ON(). The issue is, we can't free the sink_config unless we are able to find the sink device. So, if we ever end up with a sink_config with an empty mask, there is something seriously wrong and hence the WARN_ON().
> > >> cpu = cpumask_first(mask); >> sink = coresight_get_sink(etm_event_cpu_path(event_data, cpu)); >> if (sink_ops(sink)->free_buffer) >> @@ -166,7 +164,7 @@ static void *alloc_event_data(int cpu)
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>> - if (!sink_ops(sink)->alloc_buffer) >> - goto err; >> - >> + /* If we don't have any CPUs ready for tracing, abort */ >> cpu = cpumask_first(mask); >> - /* Get the AUX specific data from the sink buffer */ >> + if (cpu >= nr_cpu_ids) >> + goto err; >> + >> + /* Allocate the sink buffer for this session */ >> event_data->snk_config = >> sink_ops(sink)->alloc_buffer(sink, cpu, pages, >> nr_pages, overwrite);
Suzuki
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