Firstly, .shutdown callback may touch a uninitialized hardware
if dev->driver is set and .probe is not completed.
Secondly, device_shutdown() may dereference a null pointer to cause
oops when dev->driver is cleared after it is checked in
device_shutdown().
So just try to hold device lock and its parent lock(if it has) to
fix the races.
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
---
v2:
- take Alan's suggestion to use device_trylock to avoid
hanging during shutdown by buggy device or driver
- hold parent reference counter
drivers/base/core.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 346be8b..f2fc989 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1796,6 +1796,16 @@ out:
}
EXPORT_SYMBOL_GPL(device_move);
+static int __try_lock(struct device *dev)
+{
+ int i = 0;
+
+ while (!device_trylock(dev) && i++ < 100)
+ msleep(10);
+
+ return i < 100;
+}
+
/**
* device_shutdown - call ->shutdown() on each device to shutdown.
*/
@@ -1810,8 +1820,11 @@ void device_shutdown(void)
* devices offline, even as the system is shutting down.
*/
while (!list_empty(&devices_kset->list)) {
+ int nonlocked;
+
dev = list_entry(devices_kset->list.prev, struct device,
kobj.entry);
+ get_device(dev->parent);
get_device(dev);
/*
* Make sure the device is off the kset list, in the
@@ -1820,6 +1833,18 @@ void device_shutdown(void)
list_del_init(&dev->kobj.entry);
spin_unlock(&devices_kset->list_lock);
+ /* hold lock to avoid race with .probe/.release */
+ if (dev->parent && !__try_lock(dev->parent))
+ nonlocked = 2;
+ else if (!__try_lock(dev))
+ nonlocked = 1;
+ else
+ nonlocked = 0;
+
+ if (nonlocked)
+ dev_err(dev, "can't hold %slock for shutdown\n",
+ nonlocked == 1 ? "" : "parent ");
+
/* Don't allow any more runtime suspends */
pm_runtime_get_noresume(dev);
pm_runtime_barrier(dev);
@@ -1831,7 +1856,14 @@ void device_shutdown(void)
dev_dbg(dev, "shutdown\n");
dev->driver->shutdown(dev);
}
+
+ if (!nonlocked)
+ device_unlock(dev);
+ if (dev->parent && nonlocked != 2)
+ device_unlock(dev->parent);
+
put_device(dev);
+ put_device(dev->parent);
spin_lock(&devices_kset->list_lock);
}
--
1.7.9.5
--
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