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    SubjectRe: [PATCH] cpu/hotplug: Provide dynamic range for prepare stage
    ----- On Jan 10, 2017, at 8:01 AM, Thomas Gleixner tglx@linutronix.de wrote:

    > Mathieu reported that the LTTNG modules are broken as of 4.10-rc1 due to
    > the removal of the cpu hotplug notifiers.
    >
    > Usually I don't care much about out of tree modules, but LTTNG is widely
    > used in distros. There are two ways to solve that:
    >
    > 1) Reserve a hotplug state for LTTNG
    >
    > 2) Add a dynamic range for the prepare states.
    >
    > While #1 is the simplest solution, #2 is the proper one as we can convert
    > in tree users, which do not care about ordering, to the dynamic range as
    > well.
    >
    > Add a dynamic range which allows LTTNG to request states in the prepare
    > stage.

    I prepared a lttng-modules commit [1] that uses CPUHP_BP_PREPARE_DYN on 4.10
    kernels, and it works fine through my cpu hotplug stress-testing. It's a very
    good cleanup! Thanks Thomas for this nice API.

    I'll be able to merge my commit into lttng-modules as soon as your patch
    lands into Linux mainline.

    Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Tested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

    Thanks,

    Mathieu

    [1] https://github.com/compudj/lttng-modules-dev/commit/f02214ac2e9a0f3d8d0270c0ac702c3143cdf120

    >
    > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    >
    > ---
    >
    > diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
    > index 20bfefbe7594..d936a0021839 100644
    > --- a/include/linux/cpuhotplug.h
    > +++ b/include/linux/cpuhotplug.h
    > @@ -74,6 +74,8 @@ enum cpuhp_state {
    > CPUHP_ZCOMP_PREPARE,
    > CPUHP_TIMERS_DEAD,
    > CPUHP_MIPS_SOC_PREPARE,
    > + CPUHP_BP_PREPARE_DYN,
    > + CPUHP_BP_PREPARE_DYN_END = CPUHP_BP_PREPARE_DYN + 20,
    > CPUHP_BRINGUP_CPU,
    > CPUHP_AP_IDLE_DEAD,
    > CPUHP_AP_OFFLINE,
    > diff --git a/kernel/cpu.c b/kernel/cpu.c
    > index f75c4d031eeb..c47506357519 100644
    > --- a/kernel/cpu.c
    > +++ b/kernel/cpu.c
    > @@ -1302,10 +1302,24 @@ static int cpuhp_cb_check(enum cpuhp_state state)
    > */
    > static int cpuhp_reserve_state(enum cpuhp_state state)
    > {
    > - enum cpuhp_state i;
    > + enum cpuhp_state i, end;
    > + struct cpuhp_step *step;
    >
    > - for (i = CPUHP_AP_ONLINE_DYN; i <= CPUHP_AP_ONLINE_DYN_END; i++) {
    > - if (!cpuhp_ap_states[i].name)
    > + switch (state) {
    > + case CPUHP_AP_ONLINE_DYN:
    > + step = cpuhp_ap_states + CPUHP_AP_ONLINE_DYN;
    > + end = CPUHP_AP_ONLINE_DYN_END;
    > + break;
    > + case CPUHP_BP_PREPARE_DYN:
    > + step = cpuhp_bp_states + CPUHP_BP_PREPARE_DYN;
    > + end = CPUHP_BP_PREPARE_DYN_END;
    > + break;
    > + default:
    > + return -EINVAL;
    > + }
    > +
    > + for (i = state; i <= end; i++, step++) {
    > + if (!step->name)
    > return i;
    > }
    > WARN(1, "No more dynamic states available for CPU hotplug\n");
    > @@ -1323,7 +1337,7 @@ static int cpuhp_store_callbacks(enum cpuhp_state state,
    > const char *name,
    >
    > mutex_lock(&cpuhp_state_mutex);
    >
    > - if (state == CPUHP_AP_ONLINE_DYN) {
    > + if (state == CPUHP_AP_ONLINE_DYN || state == CPUHP_BP_PREPARE_DYN) {
    > ret = cpuhp_reserve_state(state);
    > if (ret < 0)
    > goto out;

    --
    Mathieu Desnoyers
    EfficiOS Inc.
    http://www.efficios.com

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