Re: [patch V2 11/24] ARM/hw_breakpoint: Use cpuhp_setup_state_cpuslocked()

Mark Rutland
2017-04-19T17:55:29Z

Hi,

On Tue, Apr 18, 2017 at 07:04:53PM +0200, Thomas Gleixner wrote:
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>
> arch_hw_breakpoint_init() holds get_online_cpus() while registerring the
> hotplug callbacks.
>
> cpuhp_setup_state() invokes get_online_cpus() as well. This is correct, but
> prevents the conversion of the hotplug locking to a percpu rwsem.
>
> Use cpuhp_setup_state_cpuslocked() to avoid the nested call.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: linux-arm-kernel@lists.infradead.org
>
> ---
> arch/arm/kernel/hw_breakpoint.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> --- a/arch/arm/kernel/hw_breakpoint.c
> +++ b/arch/arm/kernel/hw_breakpoint.c
> @@ -1098,8 +1098,9 @@ static int __init arch_hw_breakpoint_ini
> * assume that a halting debugger will leave the world in a nice state
> * for us.
> */
> - ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "arm/hw_breakpoint:online",
> - dbg_reset_online, NULL);
> + ret = cpuhp_setup_state_cpuslocked(CPUHP_AP_ONLINE_DYN,
> + "arm/hw_breakpoint:online",
> + dbg_reset_online, NULL);

Given the callsite, this particular change looks ok to me. So FWIW:

Acked-by: Mark Rutland <mark.rutland@arm.com>

However, as a more general note, the changes make the API feel odd. per
their current names, {get,put}_online_cpus() sound/feel like refcounting
ops, which should be able to nest.

Is there any chance these could get a better name, e.g.
{lock,unlock}_online_cpus(), so as to align with _cpuslocked?

Thanks,
Mark.