perf/core: Move perf_event_attr::sample_max_stack into perf_copy_attr()

Move the sample_max_stack check and setup into perf_copy_attr(),
so we have all perf_event_attr initial setup in one place
and can easily compare attrs in the new ioctl introduced
in following change.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Hari Bathini <hbathini@linux.vnet.ibm.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Milind Chabbi <chabbi.milind@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Oleg Nesterov <onestero@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20180312134548.31532-7-jolsa@kernel.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

kernel/events/core.c

@@ -10125,6 +10125,9 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
 			ret = -EINVAL;
 	}
 
+	if (!attr->sample_max_stack)
+		attr->sample_max_stack = sysctl_perf_event_max_stack;
+
 	if (attr->sample_type & PERF_SAMPLE_REGS_INTR)
 		ret = perf_reg_validate(attr->sample_regs_intr);
 out:
@@ -10338,9 +10341,6 @@ SYSCALL_DEFINE5(perf_event_open,
 	    perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
 		return -EACCES;
 
-	if (!attr.sample_max_stack)
-		attr.sample_max_stack = sysctl_perf_event_max_stack;
-
 	/*
 	 * In cgroup mode, the pid argument is used to pass the fd
 	 * opened to the cgroup directory in cgroupfs. The cpu argument