perf: Fix race in swevent hash

There's a race on CPU unplug where we free the swevent hash array
while it can still have events on. This will result in a
use-after-free which is BAD.

Simply do not free the hash array on unplug. This leaves the thing
around and no use-after-free takes place.

When the last swevent dies, we do a for_each_possible_cpu() iteration
anyway to clean these up, at which time we'll free it, so no leakage
will occur.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
{
	struct bpf_prog *prog;

	if (event->attr.type != PERF_TYPE_TRACEPOINT)
		return -EINVAL;

	if (event->tp_event->prog)
		return -EEXIST;

	if (!(event->tp_event->flags & TRACE_EVENT_FL_UKPROBE))
		/* bpf programs can only be attached to u/kprobes */
		return -EINVAL;

	prog = bpf_prog_get(prog_fd);
	if (IS_ERR(prog))
		return PTR_ERR(prog);

	if (prog->type != BPF_PROG_TYPE_KPROBE) {
		/* valid fd, but invalid bpf program type */
		bpf_prog_put(prog);
		return -EINVAL;
	}

	event->tp_event->prog = prog;

	return 0;
}

static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
{
	struct bpf_prog *prog;

	if (event->attr.type != PERF_TYPE_TRACEPOINT)
		return -EINVAL;

	if (event->tp_event->prog)
		return -EEXIST;

	if (!(event->tp_event->flags & TRACE_EVENT_FL_UKPROBE))
		/* bpf programs can only be attached to u/kprobes */
		return -EINVAL;

	prog = bpf_prog_get(prog_fd);
	if (IS_ERR(prog))
		return PTR_ERR(prog);

	if (prog->type != BPF_PROG_TYPE_KPROBE) {
		/* valid fd, but invalid bpf program type */
		bpf_prog_put(prog);
		return -EINVAL;
	}

	event->tp_event->prog = prog;

	return 0;
}
