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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2013-08-28 21:41:01 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2013-08-29 22:00:53 +0200
commit5e33bc4165f3edd558d9633002465a95230effc1 (patch)
treeefcc4857f4f097667a1f4e1315ffd2140078ac1d /include/linux/device.h
parentd8dfad3876e4386666b759da3c833d62fb8b2267 (diff)
driver core / ACPI: Avoid device hot remove locking issues
device_hotplug_lock is held around the acpi_bus_trim() call in acpi_scan_hot_remove() which generally removes devices (it removes ACPI device objects at least, but it may also remove "physical" device objects through .detach() callbacks of ACPI scan handlers). Thus, potentially, device sysfs attributes are removed under that lock and to remove those attributes it is necessary to hold the s_active references of their directory entries for writing. On the other hand, the execution of a .show() or .store() callback from a sysfs attribute is carried out with that attribute's s_active reference held for reading. Consequently, if any device sysfs attribute that may be removed from within acpi_scan_hot_remove() through acpi_bus_trim() has a .store() or .show() callback which acquires device_hotplug_lock, the execution of that callback may deadlock with the removal of the attribute. [Unfortunately, the "online" device attribute of CPUs and memory blocks is one of them.] To avoid such deadlocks, make all of the sysfs attribute callbacks that need to lock device hotplug, for example store_online(), use a special function, lock_device_hotplug_sysfs(), to lock device hotplug and return the result of that function immediately if it is not zero. This will cause the s_active reference of the directory entry in question to be released and the syscall to be restarted if device_hotplug_lock cannot be acquired. [show_online() actually doesn't need to lock device hotplug, but it is useful to serialize it with respect to device_offline() and device_online() for the same device (in case user space attempts to run them concurrently) which can be done with the help of device_lock().] Reported-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> Reported-and-tested-by: Gu Zheng <guz.fnst@cn.fujitsu.com> Suggested-by: Tejun Heo <tj@kernel.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Acked-by: Toshi Kani <toshi.kani@hp.com>
Diffstat (limited to 'include/linux/device.h')
-rw-r--r--include/linux/device.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/device.h b/include/linux/device.h
index 22b546a58591..545a04285120 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -895,6 +895,7 @@ static inline bool device_supports_offline(struct device *dev)
extern void lock_device_hotplug(void);
extern void unlock_device_hotplug(void);
+extern int lock_device_hotplug_sysfs(void);
extern int device_offline(struct device *dev);
extern int device_online(struct device *dev);
/*