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SubjectRe: [PATCH v1] drivers/acpi/scan.c: Document why we don't need the device_hotplug_lock
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On 7/31/2019 3:53 PM, David Hildenbrand wrote:
> Let's document why the lock is not needed in acpi_scan_init(), right now
> this is not really obvious.
>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>


> ---
>
> @Andrew, can you drop "drivers/acpi/scan.c: acquire device_hotplug_lock in
> acpi_scan_init()" and add this patch instead? Thanks
>
> ---
> drivers/acpi/scan.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 0e28270b0fd8..8444af6cd514 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -2204,6 +2204,12 @@ int __init acpi_scan_init(void)
> acpi_gpe_apply_masked_gpes();
> acpi_update_all_gpes();
>
> + /*
> + * Although we call__add_memory() that is documented to require the
> + * device_hotplug_lock, it is not necessary here because this is an
> + * early code when userspace or any other code path cannot trigger
> + * hotplug/hotunplug operations.
> + */
> mutex_lock(&acpi_scan_lock);
> /*
> * Enumerate devices in the ACPI namespace.


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