linux-kernel - [PATCH v1] drivers/acpi/scan.c: Fixup "acquire device_hotplug_lock in acpi_scan

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Message-Id: <20190731123201.13893-1-david@redhat.com>
Date:   Wed, 31 Jul 2019 14:32:01 +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: Fixup "acquire device_hotplug_lock in acpi_scan_init()"

Let's document why we take the lock here. If we're going to overhaul
memory hotplug locking, we'll have to touch many places - this comment
will help to clairfy why it was added here.

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>
---
 drivers/acpi/scan.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index cbc9d64b48dd..9193f1d46148 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -2204,6 +2204,11 @@ int __init acpi_scan_init(void)
 	acpi_gpe_apply_masked_gpes();
 	acpi_update_all_gpes();
 
+	/*
+	 * We end up calling __add_memory(), which expects the
+	 * device_hotplug_lock to be held. Races with userspace and other
+	 * hotplug activities are not really possible - lock for consistency.
+	 */
 	lock_device_hotplug();
 	mutex_lock(&acpi_scan_lock);
 
-- 
2.21.0