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[209.132.183.28]) by mx.google.com with ESMTPS id z36si452495qtz.405.2019.07.31.06.53.09 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 31 Jul 2019 06:53:09 -0700 (PDT) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CCEAB3079B62; Wed, 31 Jul 2019 13:53:08 +0000 (UTC) Received: from t460s.redhat.com (ovpn-117-240.ams2.redhat.com [10.36.117.240]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2C5081001959; Wed, 31 Jul 2019 13:53:07 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-acpi@vger.kernel.org, David Hildenbrand , "Rafael J . Wysocki" , Michal Hocko , Oscar Salvador , Andrew Morton Subject: [PATCH v1] drivers/acpi/scan.c: Document why we don't need the device_hotplug_lock Date: Wed, 31 Jul 2019 15:53:06 +0200 Message-Id: <20190731135306.31524-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Wed, 31 Jul 2019 13:53:08 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP Let's document why the lock is not needed in acpi_scan_init(), right now this is not really obvious. Cc: Rafael J. Wysocki Cc: Michal Hocko Cc: Oscar Salvador Cc: Andrew Morton Signed-off-by: David Hildenbrand Acked-by: Michal Hocko Acked-by: Rafael J. Wysocki --- @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.