lkml.org 
[lkml]   [2018]   [Sep]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] cpu/hotplug: Fix rollback during error-out in takedown_cpu()
On Tue, 4 Sep 2018, Neeraj Upadhyay wrote:
> If takedown_cpu() fails during _cpu_down(), st->state is reset,
> by calling cpuhp_reset_state(). This results in an additional
> increment of st->state, which results in CPUHP_AP_SMPBOOT_THREADS
> state being skipped during rollback. Fix this by not calling
> cpuhp_reset_state() and doing the state reset directly in
> _cpu_down().
>
> Fixes: 4dddfb5faa61 ("smp/hotplug: Rewrite AP state machine core")
> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
> ---
> kernel/cpu.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index aa7fe85..9f49edb 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -970,7 +970,14 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> */
> 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.

Thanks,

tglx























\
 
 \ /
  Last update: 2018-09-05 13:34    [W:0.084 / U:1.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site