Merge git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-for-linus

* git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-for-linus:
  stop_machine: make stop_machine_run more virtualization friendly
  doc: add a chapter about trylock functions [Bug 9011]
  modules: proper cleanup of kobject without CONFIG_SYSFS
  module loading ELF handling: use SELFMAG instead of numeric constant

Documentation/DocBook/kernel-locking.tmpl

@@ -703,6 +703,31 @@
 </sect1>
 </chapter>
 
+<chapter id="trylock-functions">
+ <title>The trylock Functions</title>
+  <para>
+   There are functions that try to acquire a lock only once and immediately
+   return a value telling about success or failure to acquire the lock.
+   They can be used if you need no access to the data protected with the lock
+   when some other thread is holding the lock. You should acquire the lock
+   later if you then need access to the data protected with the lock.
+  </para>
+
+  <para>
+    <function>spin_trylock()</function> does not spin but returns non-zero if
+    it acquires the spinlock on the first try or 0 if not. This function can
+    be used in all contexts like <function>spin_lock</function>: you must have
+    disabled the contexts that might interrupt you and acquire the spin lock.
+  </para>
+
+  <para>
+    <function>mutex_trylock()</function> does not suspend your task
+    but returns non-zero if it could lock the mutex on the first try
+    or 0 if not. This function cannot be safely used in hardware or software
+    interrupt contexts despite not sleeping.
+  </para>
+</chapter>
+
   <chapter id="Examples">
    <title>Common Examples</title>
     <para>

kernel/module.c

@@ -1337,7 +1337,19 @@ out_unreg:
 	kobject_put(&mod->mkobj.kobj);
 	return err;
 }
-#endif
+
+static void mod_sysfs_fini(struct module *mod)
+{
+	kobject_put(&mod->mkobj.kobj);
+}
+
+#else /* CONFIG_SYSFS */
+
+static void mod_sysfs_fini(struct module *mod)
+{
+}
+
+#endif /* CONFIG_SYSFS */
 
 static void mod_kobject_remove(struct module *mod)
 {
@@ -1345,7 +1357,7 @@ static void mod_kobject_remove(struct module *mod)
 	module_param_sysfs_remove(mod);
 	kobject_put(mod->mkobj.drivers_dir);
 	kobject_put(mod->holders_dir);
-	kobject_put(&mod->mkobj.kobj);
+	mod_sysfs_fini(mod);
 }
 
 /*
@@ -1780,7 +1792,7 @@ static struct module *load_module(void __user *umod,
 
 	/* Sanity checks against insmoding binaries or wrong arch,
            weird elf version */
-	if (memcmp(hdr->e_ident, ELFMAG, 4) != 0
+	if (memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0
 	    || hdr->e_type != ET_REL
 	    || !elf_check_arch(hdr)
 	    || hdr->e_shentsize != sizeof(*sechdrs)) {

kernel/stop_machine.c

@@ -62,8 +62,7 @@ static int stopmachine(void *cpu)
 		 * help our sisters onto their CPUs. */
 		if (!prepared && !irqs_disabled)
 			yield();
-		else
-			cpu_relax();
+		cpu_relax();
 	}
 
 	/* Ack: we are exiting. */
@@ -106,8 +105,10 @@ static int stop_machine(void)
 	}
 
 	/* Wait for them all to come to life. */
-	while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
+	while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads) {
 		yield();
+		cpu_relax();
+	}
 
 	/* If some failed, kill them all. */
 	if (ret < 0) {