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.
This patch fixes the order within the hot plug state machine. Signed-off-by: Richard Cochran <[email protected]> Fixes: 24f73b99716a ("timers/core: Convert to hotplug state machine") Cc: John Stultz <[email protected]> Cc: Jon Hunter <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Rasmus Villemoes <[email protected]> Cc: Sebastian Andrzej Siewior <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] --- include/linux/cpuhotplug.h | 2 +- kernel/cpu.c | 15 ++++++++++----- 2 files changed, 11 insertions(+), 6 deletions(-) diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h index 6d405db..242bf53 100644 --- a/include/linux/cpuhotplug.h +++ b/include/linux/cpuhotplug.h @@ -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, diff --git a/kernel/cpu.c b/kernel/cpu.c index 67f4943..ec12b72 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1208,11 +1208,6 @@ 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, @@ -1229,6 +1224,16 @@ 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", -- 2.1.4
