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SubjectRe: perf: fuzzer WARNING event_function_local.constprop
On Fri, Aug 12, 2016 at 12:59:11PM -0400, Vince Weaver wrote:
>
> Got this while fuzzing on the Haswell machine. It's relatively repeatable
> if anyone wants me to chase it down more.
>
> It maps to
> int ret = event_function(&efs);
> WARN_ON_ONCE(ret);
> In event_function_local()

Blergh, so I've been running perf_fuzzer for almost two hours and
_nothing_ :/

In any case, while it was running I think I've figured out how this can
happen.


Could you see if the below cures things?

---
kernel/events/core.c | 60 +++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 48 insertions(+), 12 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7090cc734a8e..406f79a6f22f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -242,18 +242,6 @@ static int event_function(void *info)
return ret;
}

-static void event_function_local(struct perf_event *event, event_f func, void *data)
-{
- struct event_function_struct efs = {
- .event = event,
- .func = func,
- .data = data,
- };
-
- int ret = event_function(&efs);
- WARN_ON_ONCE(ret);
-}
-
static void event_function_call(struct perf_event *event, event_f func, void *data)
{
struct perf_event_context *ctx = event->ctx;
@@ -303,6 +291,54 @@ static void event_function_call(struct perf_event *event, event_f func, void *da
raw_spin_unlock_irq(&ctx->lock);
}

+/*
+ * Similar to event_function_call() + event_function(), but hard assumes IRQs
+ * are already disabled and we're on the right CPU.
+ */
+static void event_function_local(struct perf_event *event, event_f func, void *data)
+{
+ struct perf_event_context *ctx = event->ctx;
+ struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
+ struct task_struct *task = READ_ONCE(ctx->task);
+ struct perf_event_context *task_ctx = NULL;
+
+ WARN_ON_ONCE(!irqs_disabled());
+
+ if (task) {
+ if (task == TASK_TOMBSTONE)
+ return;
+
+ task_ctx = ctx;
+ }
+
+ perf_ctx_lock(cpuctx, task_ctx);
+
+ task = ctx->task;
+ if (task == TASK_TOMBSTONE)
+ goto unlock;
+
+ if (task) {
+ /*
+ * We must be either inactive or active and the right task,
+ * otherwise we're screwed, since we cannot IPI to somewhere
+ * else.
+ */
+ if (ctx->is_active) {
+ if (WARN_ON_ONCE(task != current))
+ goto unlock;
+
+ if (WARN_ON_ONCE(cpuctx->task_ctx != ctx))
+ goto unlock;
+ }
+ } else {
+ WARN_ON_ONCE(&cpuctx->ctx != ctx);
+ }
+
+ func(event, cpuctx, ctx, data);
+unlock:
+ perf_ctx_unlock(cpuctx, task_ctx);
+}
+
#define PERF_FLAG_ALL (PERF_FLAG_FD_NO_GROUP |\
PERF_FLAG_FD_OUTPUT |\
PERF_FLAG_PID_CGROUP |\
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