aboutsummaryrefslogtreecommitdiffstats
path: root/kernel/reboot.c
diff options
context:
space:
mode:
authorGuenter Roeck <linux@roeck-us.net>2014-09-25 20:03:16 -0400
committerGuenter Roeck <linux@roeck-us.net>2014-09-26 03:00:06 -0400
commitb63adb979583ef185718d774d8162387db5589c0 (patch)
treee6467352881135f82037829ecdd204489fbad415 /kernel/reboot.c
parent52addcf9d6669fa439387610bc65c92fa0980cef (diff)
kernel: add support for kernel restart handler call chain
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 multiple 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. Introduce a system restart handler call chain to solve the described problems. This call chain is expected to be executed 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 call chain. By using the priority field in the notifier block, callers can control restart handler execution sequence and thus ensure that the restart handler with the optimal restart capabilities for a given system is called first. Signed-off-by: Guenter Roeck <linux@roeck-us.net> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Heiko Stuebner <heiko@sntech.de> Cc: Russell King <linux@arm.linux.org.uk> Cc: Wim Van Sebroeck <wim@iguana.be> Cc: Maxime Ripard <maxime.ripard@free-electrons.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Jonas Jensen <jonas.jensen@gmail.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Tomasz Figa <t.figa@samsung.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'kernel/reboot.c')
-rw-r--r--kernel/reboot.c81
1 files changed, 81 insertions, 0 deletions
diff --git a/kernel/reboot.c b/kernel/reboot.c
index a3a9e240fcdb..5925f5ae8dff 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -104,6 +104,87 @@ int unregister_reboot_notifier(struct notifier_block *nb)
104} 104}
105EXPORT_SYMBOL(unregister_reboot_notifier); 105EXPORT_SYMBOL(unregister_reboot_notifier);
106 106
107/*
108 * Notifier list for kernel code which wants to be called
109 * to restart the system.
110 */
111static ATOMIC_NOTIFIER_HEAD(restart_handler_list);
112
113/**
114 * register_restart_handler - Register function to be called to reset
115 * the system
116 * @nb: Info about handler function to be called
117 * @nb->priority: Handler priority. Handlers should follow the
118 * following guidelines for setting priorities.
119 * 0: Restart handler of last resort,
120 * with limited restart capabilities
121 * 128: Default restart handler; use if no other
122 * restart handler is expected to be available,
123 * and/or if restart functionality is
124 * sufficient to restart the entire system
125 * 255: Highest priority restart handler, will
126 * preempt all other restart handlers
127 *
128 * Registers a function with code to be called to restart the
129 * system.
130 *
131 * Registered functions will be called from machine_restart as last
132 * step of the restart sequence (if the architecture specific
133 * machine_restart function calls do_kernel_restart - see below
134 * for details).
135 * Registered functions are expected to restart the system immediately.
136 * If more than one function is registered, the restart handler priority
137 * selects which function will be called first.
138 *
139 * Restart handlers are expected to be registered from non-architecture
140 * code, typically from drivers. A typical use case would be a system
141 * where restart functionality is provided through a watchdog. Multiple
142 * restart handlers may exist; for example, one restart handler might
143 * restart the entire system, while another only restarts the CPU.
144 * In such cases, the restart handler which only restarts part of the
145 * hardware is expected to register with low priority to ensure that
146 * it only runs if no other means to restart the system is available.
147 *
148 * Currently always returns zero, as atomic_notifier_chain_register()
149 * always returns zero.
150 */
151int register_restart_handler(struct notifier_block *nb)
152{
153 return atomic_notifier_chain_register(&restart_handler_list, nb);
154}
155EXPORT_SYMBOL(register_restart_handler);
156
157/**
158 * unregister_restart_handler - Unregister previously registered
159 * restart handler
160 * @nb: Hook to be unregistered
161 *
162 * Unregisters a previously registered restart handler function.
163 *
164 * Returns zero on success, or %-ENOENT on failure.
165 */
166int unregister_restart_handler(struct notifier_block *nb)
167{
168 return atomic_notifier_chain_unregister(&restart_handler_list, nb);
169}
170EXPORT_SYMBOL(unregister_restart_handler);
171
172/**
173 * do_kernel_restart - Execute kernel restart handler call chain
174 *
175 * Calls functions registered with register_restart_handler.
176 *
177 * Expected to be called from machine_restart as last step of the restart
178 * sequence.
179 *
180 * Restarts the system immediately if a restart handler function has been
181 * registered. Otherwise does nothing.
182 */
183void do_kernel_restart(char *cmd)
184{
185 atomic_notifier_call_chain(&restart_handler_list, reboot_mode, cmd);
186}
187
107void migrate_to_reboot_cpu(void) 188void migrate_to_reboot_cpu(void)
108{ 189{
109 /* The boot cpu is always logical cpu 0 */ 190 /* The boot cpu is always logical cpu 0 */