warn when statically-allocated kobjects are used

One of the top ten sysfs problems is that users use statically
allocated kobjects.  This patch reminds them that this is a
naughty thing.

One _really_ nice thing this patch does, is us the kallsyms
mechanism to print out exactly which symbol is being complained
about:

	The kobject at, or inside 'statickobj.2'@(0xc040d020) is not dynamically allocated.

This patch replaces the previous implementation's use of a
_sdata symbol in favor of using kallsyms_lookup().  If a
kobject's address is a resolvable symbol, then it isn't
dynamically allocated.

The one exception to this is init symbols.  The patch also
checks to see whether __init memory has been freed and if
it has will allow kobjects in those sections.

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

3 files changed, 62 insertions, 0 deletions

diff --git a/include/linux/init.h b/include/linux/init.h
index 21d658cdfa27..b1ed48ddf73f 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -142,6 +142,7 @@ extern initcall_t __security_initcall_start[], __security_initcall_end[];
 extern char __initdata boot_command_line[];
 extern char *saved_command_line;
 extern unsigned int reset_devices;
+extern int initmem_now_dynamic;
 
 /* used by init/main.c */
 void setup_arch(char **);
diff --git a/init/main.c b/init/main.c
index a87d4ca5c36c..3ae95abe0f7f 100644
--- a/init/main.c
+++ b/init/main.c
@@ -788,12 +788,21 @@ static void run_init_process(char *init_filename)
 	kernel_execve(init_filename, argv_init, envp_init);
 }
 
+/*
+ * __init/__init_data sections are turned into normal
+ * dynamically allocated memory later in boot.  When
+ * this is 0, the memory is for the __init purposes,
+ * when it it some other value, the memory is dynamic.
+ */
+int initmem_now_dynamic;
+
 /* This is a non __init function. Force it to be noinline otherwise gcc
  * makes it inline to init() and it becomes part of init.text section
  */
 static int noinline init_post(void)
 {
 	free_initmem();
+	initmem_now_dynamic = 1;
 	unlock_kernel();
 	mark_rodata_ro();
 	system_state = SYSTEM_RUNNING;
diff --git a/lib/kobject.c b/lib/kobject.c
index 718e5101c263..bd0689d639a0 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -17,6 +17,57 @@
 #include <linux/module.h>
 #include <linux/stat.h>
 #include <linux/slab.h>
+#include <linux/kallsyms.h>
+#include <asm-generic/sections.h>
+
+#ifdef CONFIG_X86_32
+static int ptr_in_range(void *ptr, void *start, void *end)
+{
+	/*
+	 * This should hopefully get rid of causing warnings
+	 * if the architecture did not set one of the section
+	 * variables up.
+	 */
+	if (start >= end)
+		return 0;
+
+	if ((ptr >= start) && (ptr < end))
+		return 1;
+	return 0;
+}
+
+static void verify_dynamic_kobject_allocation(struct kobject *kobj)
+{
+	char *namebuf;
+	const char *ret;
+
+	namebuf = kzalloc(KSYM_NAME_LEN, GFP_KERNEL);
+	ret = kallsyms_lookup((unsigned long)kobj, NULL, NULL, NULL,
+			namebuf);
+	/*
+	 * This is the X86_32-only part of this function.
+	 * This is here because it is valid to have a kobject
+	 * in an __init section, but only after those
+	 * sections have been freed back to the dynamic pool.
+	 */
+	if (!initmem_now_dynamic &&
+	    ptr_in_range(kobj, __init_begin, __init_end))
+		goto out;
+	if (!ret || !strlen(ret))
+		goto out;
+	pr_debug("---- begin silly warning ----\n");
+	pr_debug("This is a janitorial warning, not a kernel bug.\n");
+	pr_debug("The kobject '%s', at, or inside '%s'@(0x%p) is not "
+		 "dynamically allocated.\n", kobject_name(kobj), namebuf, kobj);
+	pr_debug("kobjects must be dynamically allocated, not static\n");
+	/* dump_stack(); */
+	pr_debug("---- end silly warning ----\n");
+out:
+	kfree(namebuf);
+}
+#else
+static void verify_dynamic_kobject_allocation(struct kobject *kobj) { }
+#endif
 
 /*
  * populate_dir - populate directory with attributes.
@@ -278,6 +329,7 @@ void kobject_init(struct kobject *kobj, struct kobj_type *ktype)
 		       "object, something is seriously wrong.\n", kobj);
 		dump_stack();
 	}
+	verify_dynamic_kobject_allocation(kobj);
 
 	kobject_init_internal(kobj);
 	kobj->ktype = ktype;