[PATCH] Don't attempt to power off if power off is not implemented

The problem.  It is expected that /sbin/halt -p works exactly like
/sbin/halt, when the kernel does not implement power off functionality.

The kernel can do a lot of work in the reboot notifiers and in
device_shutdown before we even get to machine_power_off.  Some of that
shutdown is not safe if you are leaving the power on, and it definitely
gets in the way of using sysrq or pressing ctrl-alt-del.  Since the
shutdown happens in generic code there is no way to fix this in
architecture specific code :(

Some machines are kernel oopsing today because of this.

The simple solution is to turn LINUX_REBOOT_CMD_POWER_OFF into
LINUX_REBOOT_CMD_HALT if power_off functionality is not implemented.

This has the unfortunate side effect of disabling the power off
functionality on architectures that leave pm_power_off to null and still
implement something in machine_power_off.  And it will break the build on
some architectures that don't have a pm_power_off variable at all.

On both counts I say tough.

For architectures like alpha that don't implement the pm_power_off variable
pm_power_off is declared in linux/pm.h and it is a generic part of our
power management code, and all architectures should implement it.

For architectures like parisc that have a default power off method in
machine_power_off if pm_power_off is not implemented or fails.  It is easy
enough to set the pm_power_off variable.  And nothing bad happens there,
the machines just stop powering off.

The current semantics are impossible without a flag at the top level so we
can avoid the problem code if a power off is not implemented.  pm_power_off
is as good a flag as any with the bonus that it works without modification
on at least x86, x86_64, powerpc, and ppc today.

Andrew can you pick this up and put this in the mm tree.  Kernels that
don't compile or don't power off seem saner than kernels that oops or
panic.  Until we get the arch specific patches for the problem
architectures this probably isn't smart to push into the stable kernel.
Unfortunately I don't have the time at the moment to walk through every
architecture and make them work.  And even if I did I couldn't test it :(

From: Hirokazu Takata <takata@linux-m32r.org>

    Add pm_power_off() for build fix of arch/m32r/kernel/process.c.

From: Miklos Szeredi <miklos@szeredi.hu>

    UML build fix

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Hayato Fujiwara <fujiwara@linux-m32r.org>
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index a8682612abc0d8ce46c1979a48b4b6d78f31b7b0..abb739b88ed15603400495cd6cadab48ff63a1ac 100644 (file)
--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -43,6 +43,11 @@
 #include "proto.h"
 #include "pci_impl.h"
 
+/*
+ * Power off function, if any
+ */
+void (*pm_power_off)(void) = machine_power_off;
+
 void
 cpu_idle(void)
 {

diff --git a/arch/m32r/kernel/process.c b/arch/m32r/kernel/process.c
index cc4b571e5db715c1fba35eab7ce3ee0d1e6784ef..3bf55d92933f62f635c1c1be3290f5fa13cc4348 100644 (file)
--- a/arch/m32r/kernel/process.c
+++ b/arch/m32r/kernel/process.c
@@ -50,6 +50,10 @@ unsigned long thread_saved_pc(struct task_struct *tsk)
  * Powermanagement idle function, if any..
  */
 void (*pm_idle)(void) = NULL;
+EXPORT_SYMBOL(pm_idle);
+
+void (*pm_power_off)(void) = NULL;
+EXPORT_SYMBOL(pm_power_off);
 
 void disable_hlt(void)
 {

diff --git a/arch/um/kernel/reboot.c b/arch/um/kernel/reboot.c
index a637e885c5835cb7c78e31c6d40099f8473c448c..6f1a3a288117985e1b4bc9d73bda578284c26d09 100644 (file)
--- a/arch/um/kernel/reboot.c
+++ b/arch/um/kernel/reboot.c
@@ -12,6 +12,8 @@
 #include "mode.h"
 #include "choose-mode.h"
 
+void (*pm_power_off)(void);
+
 #ifdef CONFIG_SMP
 static void kill_idlers(int me)
 {

diff --git a/kernel/sys.c b/kernel/sys.c
index eecf84526afeca15c7e82894c5c3e898239fa062..d8e49e659027f70de633b69d2efd13132a428bb5 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -489,6 +489,12 @@ asmlinkage long sys_reboot(int magic1, int magic2, unsigned int cmd, void __user
                        magic2 != LINUX_REBOOT_MAGIC2C))
                return -EINVAL;
 
+       /* Instead of trying to make the power_off code look like
+        * halt when pm_power_off is not set do it the easy way.
+        */
+       if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off)
+               cmd = LINUX_REBOOT_CMD_HALT;
+
        lock_kernel();
        switch (cmd) {
        case LINUX_REBOOT_CMD_RESTART: