On 07/07/2014 02:14 PM, Andrew Morton wrote:
On Sun, 6 Jul 2014 16:38:14 -0700 Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
Various drivers implement architecture and/or device specific means
to restart (reset) the system. Various mechanisms have been implemented
to support those schemes. The best known mechanism is arm_pm_restart,
which is a function pointer to be set either from platform specific code
or from drivers. Another mechanism is to use hardware watchdogs to issue
a reset; this mechanism is used if there is no other method available
to reset a board or system. Two examples are alim7101_wdt, which currently
uses the reboot notifier to trigger a reset, and moxart_wdt, which registers
the arm_pm_restart function.
The existing mechanisms have a number of drawbacks. Typically only one scheme
to restart the system is supported (at least if arm_pm_restart is used).
At least in theory there can be mutliple means to restart the system, some of
which may be less desirable (for example one mechanism may only reset the CPU,
while another may reset the entire system). Using arm_pm_restart can also be
racy if the function pointer is set from a driver, as the driver may be in
the process of being unloaded when arm_pm_restart is called.
Using the reboot notifier is always racy, as it is unknown if and when
other functions using the reboot notifier have completed execution
by the time the watchdog fires.
To solve the problem, introduce a system restart notifier. This notifier
is expected to be called from the architecture specific machine_restart()
function. Drivers providing system restart functionality (such as the watchdog
drivers mentioned above) are expected to register with this notifier.
It all looks sane to my unfamiliar eye.
/*
+ * Notifier list for kernel code which wants to be called
+ * to restart the system.
+ */
hm, is this all we have to say?
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -104,6 +104,38 @@ int unregister_reboot_notifier(struct notifier_block *nb)
}
EXPORT_SYMBOL(unregister_reboot_notifier);
+/**
+ * register_restart_notifier - Register function to be called to reset
+ * the system
+ * @nb: Info about notifier function to be called
+ *
+ * Registers a function with the list of functions
+ * to be called to restart the system.
+ *
+ * Currently always returns zero, as blocking_notifier_chain_register()
+ * always returns zero.
+ */
This would be a good place to describe what those notifier callbacks
actually do. Why they exist, what their role is, under what
circumstances they are called, what values they should return, etc.
Makes sense. Done.
Guenter
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