Re: [PATCH 1/2] xfs: introduce CPU hotplug infrastructure

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Jun 07, 2021 at 10:17:14AM +1000, Dave Chinner wrote:
> 
> From: Dave Chinner <dchinner@redhat.com>
> 
> We need to move to per-cpu state for CIL tracking, but to do that we
> need to handle CPUs being removed from the system by the hot-plug
> code. Introduce generic XFS infrastructure to handle CPU hotplug
> events that is set up at module init time and torn down at module
> exit time.
> 
> Initially, the CIL only needs CPU dead notifications, so we only set
> up a callback for these notifications. The infrastructure can be
> updated in future for CPU add notifications easily if every needed.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Looks good,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/xfs/xfs_super.c         | 38 +++++++++++++++++++++++++++++++++++++-
>  include/linux/cpuhotplug.h |  1 +
>  2 files changed, 38 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 017ba9c24c2d..0146d3c89da9 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -2123,6 +2123,35 @@ xfs_destroy_workqueues(void)
>  	destroy_workqueue(xfs_alloc_wq);
>  }
>  
> +static int
> +xfs_cpu_dead(
> +	unsigned int		cpu)
> +{
> +	return 0;
> +}
> +
> +static int __init
> +xfs_cpu_hotplug_init(void)
> +{
> +	int	error;
> +
> +	error = cpuhp_setup_state_nocalls(CPUHP_XFS_DEAD,
> +					"xfs:dead", NULL,
> +					xfs_cpu_dead);
> +	if (error < 0) {
> +		xfs_alert(NULL,
> +"Failed to initialise CPU hotplug, error %d. XFS is non-functional.",
> +			error);
> +	}
> +	return error;
> +}
> +
> +static void
> +xfs_cpu_hotplug_destroy(void)
> +{
> +	cpuhp_remove_state_nocalls(CPUHP_XFS_DEAD);
> +}
> +
>  STATIC int __init
>  init_xfs_fs(void)
>  {
> @@ -2135,10 +2164,14 @@ init_xfs_fs(void)
>  
>  	xfs_dir_startup();
>  
> -	error = xfs_init_zones();
> +	error = xfs_cpu_hotplug_init();
>  	if (error)
>  		goto out;
>  
> +	error = xfs_init_zones();
> +	if (error)
> +		goto out_destroy_hp;
> +
>  	error = xfs_init_workqueues();
>  	if (error)
>  		goto out_destroy_zones;
> @@ -2218,6 +2251,8 @@ init_xfs_fs(void)
>  	xfs_destroy_workqueues();
>   out_destroy_zones:
>  	xfs_destroy_zones();
> + out_destroy_hp:
> +	xfs_cpu_hotplug_destroy();
>   out:
>  	return error;
>  }
> @@ -2240,6 +2275,7 @@ exit_xfs_fs(void)
>  	xfs_destroy_workqueues();
>  	xfs_destroy_zones();
>  	xfs_uuid_table_free();
> +	xfs_cpu_hotplug_destroy();
>  }
>  
>  module_init(init_xfs_fs);
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index 4a62b3980642..bf8f29ad9bf8 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -52,6 +52,7 @@ enum cpuhp_state {
>  	CPUHP_FS_BUFF_DEAD,
>  	CPUHP_PRINTK_DEAD,
>  	CPUHP_MM_MEMCQ_DEAD,
> +	CPUHP_XFS_DEAD,
>  	CPUHP_PERCPU_CNT_DEAD,
>  	CPUHP_RADIX_DEAD,
>  	CPUHP_PAGE_ALLOC_DEAD,