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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Pingfan Liu <kernelfans@gmail.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.9 043/111] drivers/base: stop new probing during shutdown
Date:   Mon, 24 Sep 2018 13:52:10 +0200
Message-Id: <20180924113109.233881162@linuxfoundation.org>
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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Pingfan Liu <kernelfans@gmail.com>

[ Upstream commit 3297c8fc65af5d40501ea7cddff1b195cae57e4e ]

There is a race window in device_shutdown(), which may cause
-1. parent device shut down before child or
-2. no shutdown on a new probing device.

For 1st, taking the following scenario:
         device_shutdown                        new plugin device
  list_del_init(parent_dev);
  spin_unlock(list_lock);
                                                  device_add(child)
                                                  probe child
  shutdown parent_dev
       --> now child is on the tail of devices_kset

For 2nd, taking the following scenario:
         device_shutdown                        new plugin device
                                                  device_add(dev)
  device_lock(dev);
  ...
  device_unlock(dev);
                                                  probe dev
       --> now, the new occurred dev has no opportunity to shutdown

To fix this race issue, just prevent the new probing request. With this
logic, device_shutdown() is more similar to dpm_prepare().

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/base/core.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2072,6 +2072,9 @@ void device_shutdown(void)
 {
 	struct device *dev, *parent;
 
+	wait_for_device_probe();
+	device_block_probing();
+
 	spin_lock(&devices_kset->list_lock);
 	/*
 	 * Walk the devices list backward, shutting down each in turn.