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authorThomas Gleixner <tglx@linutronix.de>2016-03-10 20:42:08 +0100
committerThomas Gleixner <tglx@linutronix.de>2016-03-10 21:21:59 +0100
commit2a58c527bb566b7abad96289fa5b973040c33c82 (patch)
tree5f22c738d4a79fb4ed816e3453445f55d0e6626e /kernel/cpu.c
parent5d8eb84253333f8f63ec704276e3f0a8ec8f3189 (diff)
cpu/hotplug: Fix smpboot thread ordering
Commit 931ef163309e moved the smpboot thread park/unpark invocation to the state machine. The move of the unpark invocation was premature as it depends on work in progress patches. As a result cpu down can fail, because rcu synchronization in takedown_cpu() eventually requires a functional softirq thread. I never encountered the problem in testing, but 0day testing managed to provide a reliable reproducer. Remove the smpboot_threads_park() call from the state machine for now and put it back into the original place after the rcu synchronization. I'm embarrassed as I knew about the dependency and still managed to get it wrong. Hotplug induced brain melt seems to be the only sensible explanation for that. Fixes: 931ef163309e "cpu/hotplug: Unpark smpboot threads from the state machine" Reported-by: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org>
Diffstat (limited to 'kernel/cpu.c')
-rw-r--r--kernel/cpu.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 373e831e0faa..bcee286b7c73 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -706,8 +706,9 @@ static int takedown_cpu(unsigned int cpu)
else
synchronize_rcu();
- /* Park the hotplug thread */
+ /* Park the smpboot threads */
kthread_park(per_cpu_ptr(&cpuhp_state, cpu)->thread);
+ smpboot_park_threads(cpu);
/*
* Prevent irq alloc/free while the dying cpu reorganizes the
@@ -1206,7 +1207,7 @@ static struct cpuhp_step cpuhp_ap_states[] = {
[CPUHP_AP_SMPBOOT_THREADS] = {
.name = "smpboot:threads",
.startup = smpboot_unpark_threads,
- .teardown = smpboot_park_threads,
+ .teardown = NULL,
},
[CPUHP_AP_NOTIFY_ONLINE] = {
.name = "notify:online",