linux-kernel - [PATCH v1] drivers/acpi/scan.c: Document why we don't need the device_hotplug

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Date:   Wed, 31 Jul 2019 15:53:06 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linux-acpi@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Michal Hocko <mhocko@...e.com>,
        Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH v1] drivers/acpi/scan.c: Document why we don't need the device_hotplug_lock

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@...el.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: David Hildenbrand <david@...hat.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.
-- 
2.21.0