Messages in this thread | | | Subject | Re: [PATCH] cpu/hotplug: Fix rollback during error-out in takedown_cpu() | From | Neeraj Upadhyay <> | Date | Wed, 5 Sep 2018 18:21:13 +0530 |
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On 09/05/2018 05:53 PM, Thomas Gleixner wrote: > On Wed, 5 Sep 2018, Thomas Gleixner wrote: >> On Tue, 4 Sep 2018, Neeraj Upadhyay wrote: >>> ret = cpuhp_down_callbacks(cpu, st, target); >>> if (ret && st->state > CPUHP_TEARDOWN_CPU && st->state < prev_state) { >>> - cpuhp_reset_state(st, prev_state); >>> + /* >>> + * As st->last is not set, cpuhp_reset_state() increments >>> + * st->state, which results in CPUHP_AP_SMPBOOT_THREADS being >>> + * skipped during rollback. So, don't use it here. >>> + */ >>> + st->rollback = true; >>> + st->target = prev_state; >>> + st->bringup = !st->bringup; >> No, this is just papering over the actual problem. >> >> The state inconsistency happens in take_cpu_down() when it returns with a >> failure from __cpu_disable() because that returns with state = TEARDOWN_CPU >> and st->state is then incremented in undo_cpu_down(). >> >> That's the real issue and we need to analyze the whole cpu_down rollback >> logic first. > And looking closer this is a general issue. Just that the TEARDOWN state > makes it simple to observe. It's universaly broken, when the first teardown > callback fails because, st->state is only decremented _AFTER_ the callback > returns success, but undo_cpu_down() increments unconditionally. > > Patch below. > > Thanks, > > tglx As per my understanding, there are 2 problems here; one is fixed with your patch, and other is cpuhp_reset_state() is used during rollback from non-AP to AP state, which seem to result in 2 increments of st->state (one increment done by cpuhp_reset_state() and another by cpu_thread_fun()) . > ---- > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -916,7 +916,8 @@ static int cpuhp_down_callbacks(unsigned > ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL); > if (ret) { > st->target = prev_state; > - undo_cpu_down(cpu, st); > + if (st->state < prev_state) > + undo_cpu_down(cpu, st); > break; > } > } > @@ -969,7 +970,7 @@ static int __ref _cpu_down(unsigned int > * to do the further cleanups. > */ > ret = cpuhp_down_callbacks(cpu, st, target); > - if (ret && st->state > CPUHP_TEARDOWN_CPU && st->state < prev_state) { > + if (ret && st->state == CPUHP_TEARDOWN_CPU && st->state < prev_state) { > cpuhp_reset_state(st, prev_state); > __cpuhp_kick_ap(st); > }
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