percpu: use notrace variant of preempt_disable/preempt_enable

Commit 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like
events do") added a couple of this_cpu_read calls to the ftrace code.

On x86 this is not a problem, since it has single instructions to read
percpu data. Other architectures which use the generic variant now
have additional preempt_disable and preempt_enable calls in the core
ftrace code. This may lead to recursive calls and in result to a dead
machine, e.g. if preemption and debugging options are enabled.

To fix this use the notrace variant of preempt_disable and
preempt_enable within the generic percpu code.

Reported-and-bisected-by: Sebastian Ott <[e-mail]>
Tested-by: Sebastian Ott <[e-mail]>
Fixes: 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like events do")
Signed-off-by: Heiko Carstens <[e-mail]>
Acked-by: Steven Rostedt <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

include/asm-generic/percpu.h

···
 #define this_cpu_generic_read(pcp)					\
 ({									\
 	typeof(pcp) __ret;						\
-	preempt_disable();						\
+	preempt_disable_notrace();					\
 	__ret = raw_cpu_generic_read(pcp);				\
-	preempt_enable();						\
+	preempt_enable_notrace();					\
 	__ret;								\
 })