tick/broadcast: Prevent deadlock on tick_broadcast_lock

tick_broadcast_lock is taken from interrupt context, but the following call
chain takes the lock without disabling interrupts:

[   12.703736]  _raw_spin_lock+0x3b/0x50
[   12.703738]  tick_broadcast_control+0x5a/0x1a0
[   12.703742]  intel_idle_cpu_online+0x22/0x100
[   12.703744]  cpuhp_invoke_callback+0x245/0x9d0
[   12.703752]  cpuhp_thread_fun+0x52/0x110
[   12.703754]  smpboot_thread_fn+0x276/0x320

So the following deadlock can happen:

   lock(tick_broadcast_lock);
   <Interrupt>
      lock(tick_broadcast_lock);

intel_idle_cpu_online() is the only place which violates the calling
convention of tick_broadcast_control(). This was caused by the removal of
the smp function call in course of the cpu hotplug rework.

Instead of slapping local_irq_disable/enable() at the call site, we can
relax the calling convention and handle it in the core code, which makes
the whole machinery more robust.

Fixes: 29d7bbad ("intel_idle: Remove superfluous SMP fuction call")
Reported-by: Gabriel C <nix.or.die@gmail.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Cc: Ruslan Ruslichenko <rruslich@cisco.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: lwn@lwn.net
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: stable <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/1486953115.5912.4.camel@gmx.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>