From 4fae16dffb812f0e0d98a0b2b0856ca48ca63e6c Mon Sep 17 00:00:00 2001 From: Richard Cochran Date: Wed, 27 Jul 2016 11:08:18 +0200 Subject: 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 Reported-by: kbuild test robot Fixes: 24f73b99716a ("timers/core: Convert to hotplug state machine") Signed-off-by: Richard Cochran Cc: Peter Zijlstra Cc: Sebastian Andrzej Siewior Cc: Rasmus Villemoes Cc: John Stultz Cc: rt@linutronix.de Cc: Oleg Nesterov Cc: Linus Torvalds Link: http://lkml.kernel.org/r/1469610498-25914-1-git-send-email-rcochran@linutronix.de Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar --- kernel/cpu.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index f24f45915b54..341bf80f80bd 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -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", -- cgit v1.2.3-55-g7522