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Date:   Sun, 25 Jun 2000 01:30:50 +1000
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From:   Andrew Morton <andrewm@uow.edu.au>
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Subject: Re: modular net drivers
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            <3954262D.60BDEF41@uow.edu.au> <20000624080106.A25102@fruits.uzix.org>
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OK. I've flung together a prototype.

It doesn't immediately crash....
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 name="freeze.patch"
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 filename="freeze.patch"

--- linux-official/kernel/module.c	Fri Jun  9 23:00:28 2000
+++ linux-akpm/kernel/module.c	Sun Jun 25 01:15:57 2000
@@ -365,17 +365,14 @@
 	return res;
 }
 
-asmlinkage long
-sys_delete_module(const char *name_user)
+static long
+do_sys_delete_module(const char *name_user)
 {
 	struct module *mod, *next;
 	char *name;
 	long error;
 	int something_changed;
 
-	if (!capable(CAP_SYS_MODULE))
-		return -EPERM;
-
 	lock_kernel();
 	if (name_user) {
 		if ((error = get_mod_name(name_user, &name)) < 0)
@@ -442,6 +439,75 @@
 	unlock_kernel();
 	return error;
 }
+
+#ifdef CONFIG_SMP
+static volatile int ice_block;
+static spinlock_t freeze_lock = SPIN_LOCK_UNLOCKED;
+
+static int
+antarctica(void *dummy)
+{
+	printk("start antarctica on %d\n", smp_processor_id());
+	while (ice_block)
+		;
+	printk("stop antarctica on %d\n", smp_processor_id());
+	return 0;
+}
+
+static int
+freeze_other_cpus(void)
+{
+	int cpu, retval;
+
+	if (!spin_trylock(&freeze_lock))
+		return -EAGAIN;
+
+	printk("start freeze_other_cpus()\n");
+	ice_block = 1;
+	for (cpu = 0; cpu < smp_num_cpus - 1; cpu++) {
+		retval = kernel_thread(antarctica, (void *)0, 0);
+		if (retval < 0)
+			goto out_melt;
+	}
+	printk("continue freeze_other_cpus()\n");
+	return 0;
+out_melt:
+	ice_block = 0;
+	spin_unlock(&freeze_lock);
+	return retval;
+}
+
+static void
+melt_other_cpus(void)
+{
+	printk("melt_other_cpus() starts\n");
+	ice_block = 0;
+	spin_unlock(&freeze_lock);
+	printk("melt_other_cpus() stops\n");
+}
+
+#else	/* CONFIG_SMP */
+
+#define freeze_other_cpus() 0
+#define melt_other_cpus() do { } while (0)
+#endif
+
+asmlinkage long
+sys_delete_module(const char *name_user)
+{
+	long ret;
+
+	if (!capable(CAP_SYS_MODULE))
+		return -EPERM;
+
+	if ((ret = freeze_other_cpus()))
+		return ret;
+
+	ret = do_sys_delete_module(name_user);
+	melt_other_cpus();
+	return ret;
+}
+
 
 /* Query various bits about modules.  */
 

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