On Wed, Sep 05, 2018 at 11:22:07AM +0530, Neeraj Upadhyay wrote:
> The smp_mb() in cpuhp_thread_fun() appears to be misplaced, and
> need to be after the load of st->should_run, to prevent
> reordering of the later load/stores w.r.t. the load of
> st->should_run.
I'm tempted to say this changelog needs improvement, but given the
comment that goes with the smp_mb(), yes this is obviously right.
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxx>
> Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
> ---
> kernel/cpu.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index aa7fe85..eb4041f 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -607,15 +607,15 @@ static void cpuhp_thread_fun(unsigned int cpu)
> bool bringup = st->bringup;
> enum cpuhp_state state;
>
> + if (WARN_ON_ONCE(!st->should_run))
> + return;
> +
> /*
> * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
> * that if we see ->should_run we also see the rest of the state.
> */
> smp_mb();
>
> - if (WARN_ON_ONCE(!st->should_run))
> - return;
> -
> cpuhp_lock_acquire(bringup);
>
> if (st->single) {
