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| author | Thomas Gleixner <tglx@linutronix.de> | 2016-03-10 20:42:08 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2016-03-10 21:21:59 +0100 |
| commit | 2a58c527bb566b7abad96289fa5b973040c33c82 (patch) | |
| tree | 5f22c738d4a79fb4ed816e3453445f55d0e6626e /kernel/cpu.c | |
| parent | cpu/hotplug: Remove redundant state check (diff) | |
| download | linux-2a58c527bb566b7abad96289fa5b973040c33c82.tar.xz linux-2a58c527bb566b7abad96289fa5b973040c33c82.zip | |
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.c | 5 |
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", |