Commit 4fae16df authored Jul 27, 2016 by Richard Cochran Committed by Ingo Molnar Jul 28, 2016

timers/core: Correct callback order during CPU hot plug



On the tear-down path, the dead CPU callback for the timers was
misplaced within the 'cpuhp_state' enumeration.  There is a hidden
dependency between the timers and block multiqueue.  The timers
callback must happen before the block multiqueue callback otherwise a
RCU stall occurs.

Move the timers callback to the proper place in the state machine.

Reported-and-tested-by: Jon Hunter <jonathanh@nvidia.com>
Reported-by: kbuild test robot <lkp@intel.com>
Fixes: 24f73b99 ("timers/core: Convert to hotplug state machine")
Signed-off-by: Richard Cochran <rcochran@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: John Stultz <john.stultz@linaro.org>
Cc: rt@linutronix.de
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1469610498-25914-1-git-send-email-rcochran@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent cd894f14

include/linux/cpuhotplug.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -20,9 +20,9 @@ enum cpuhp_state {
		CPUHP_PROFILE_PREPARE,
		CPUHP_X2APIC_PREPARE,
		CPUHP_SMPCFD_PREPARE,
		CPUHP_TIMERS_DEAD,
		CPUHP_RCUTREE_PREP,
		CPUHP_NOTIFY_PREPARE,
		CPUHP_TIMERS_DEAD,
		CPUHP_BRINGUP_CPU,
		CPUHP_AP_IDLE_DEAD,
		CPUHP_AP_OFFLINE,

kernel/cpu.c

+10 −5

Original line number	Diff line number	Diff line
		@@ -1200,11 +1200,6 @@ static struct cpuhp_step cpuhp_bp_states[] = {
		.startup = smpcfd_prepare_cpu,
		.teardown = smpcfd_dead_cpu,
		},
		[CPUHP_TIMERS_DEAD] = {
		.name = "timers dead",
		.startup = NULL,
		.teardown = timers_dead_cpu,
		},
		[CPUHP_RCUTREE_PREP] = {
		.name = "RCU-tree prepare",
		.startup = rcutree_prepare_cpu,
		@@ -1221,6 +1216,16 @@ static struct cpuhp_step cpuhp_bp_states[] = {
		.skip_onerr = true,
		.cant_stop = true,
		},
		/*
		* On the tear-down path, timers_dead_cpu() must be invoked
		* before blk_mq_queue_reinit_notify() from notify_dead(),
		* otherwise a RCU stall occurs.
		*/
		[CPUHP_TIMERS_DEAD] = {
		.name = "timers dead",
		.startup = NULL,
		.teardown = timers_dead_cpu,
		},
		/* Kicks the plugged cpu into life */
		[CPUHP_BRINGUP_CPU] = {
		.name = "cpu:bringup",

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