x86/mce: Make timer handling more robust

Erik reported that on a preproduction hardware a CMCI storm triggers the
BUG_ON in add_timer_on(). The reason is that the per CPU MCE timer is
started by the CMCI logic before the MCE CPU hotplug callback starts the
timer with add_timer_on(). So the timer is already queued which triggers
the BUG.

Using add_timer_on() is pretty pointless in this code because the timer is
strictlty per CPU, initialized as pinned and all operations which arm the
timer happen on the CPU to which the timer belongs.

Simplify the whole machinery by using mod_timer() instead of add_timer_on()
which avoids the problem because mod_timer() can handle already queued
timers. Use __start_timer() everywhere so the earliest armed expiry time is
preserved.

Reported-by: Erik Veijola <erik.veijola@intel.com>
Tested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@alien8.de>
Cc: Tony Luck <tony.luck@intel.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1701310936080.3457@nanos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

path: root/net/6lowpan/nhc_hop.c

/*
 *	6LoWPAN IPv6 Hop-by-Hop Options Header compression according to RFC6282
 *
 *	This program is free software; you can redistribute it and/or
 *	modify it under the terms of the GNU General Public License
 *	as published by the Free Software Foundation; either version
 *	2 of the License, or (at your option) any later version.
 */

#include "nhc.h"

#define LOWPAN_NHC_HOP_IDLEN	1
#define LOWPAN_NHC_HOP_ID_0	0xe0
#define LOWPAN_NHC_HOP_MASK_0	0xfe

static void hop_nhid_setup(struct lowpan_nhc *nhc)
{
	nhc->id[0] = LOWPAN_NHC_HOP_ID_0;
	nhc->idmask[0] = LOWPAN_NHC_HOP_MASK_0;
}

LOWPAN_NHC(nhc_hop, "RFC6282 Hop-by-Hop Options", NEXTHDR_HOP, 0,
	   hop_nhid_setup, LOWPAN_NHC_HOP_IDLEN, NULL, NULL);

module_lowpan_nhc(nhc_hop);
MODULE_DESCRIPTION("6LoWPAN next header RFC6282 Hop-by-Hop Options compression");
MODULE_LICENSE("GPL");