[v2,2/2] dyndbg: use the module notifier callbacks

Commit Message

Jason Baron Feb. 28, 2023, 7:35 p.m. UTC

As part of Jim Cromie's new dynamic debug classmap feature, the new code
tries to toggle a jump label from dynamic_debug_setup(). However,
dynamic_debug_setup() is called before the 'module_notify_list' notifier
chain is invoked. And jump labels are initialized via the module notifier
chain. Note this is an issue for a new feature not yet merged and doesn't
affect any existing codepaths.

We could just move dynamic_debug_setup() earlier in load_module(). But
let's instead ensure the ordering via the 'priority' in the module list
notifier. This brings dynamic debug more in line with other subsystems and
pulls code out of the core module code.

Link: https://lore.kernel.org/lkml/[e-mail]/
Reported-by: kernel test robot <[e-mail]>
Link: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Tested-by: Jim Cromie <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
CC: Jim Cromie <[e-mail]>
Cc: Luis Chamberlain <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Jason Baron <[e-mail]>
---
 include/linux/dynamic_debug.h | 13 ---------
 include/linux/module.h        |  4 +++
 kernel/module/internal.h      |  2 --
 kernel/module/main.c          | 30 ++++++---------------
 lib/dynamic_debug.c           | 50 ++++++++++++++++++++++++++++-------
 5 files changed, 53 insertions(+), 46 deletions(-)

Comments

Luis Chamberlain Feb. 28, 2023, 8:44 p.m. UTC | #1

On Tue, Feb 28, 2023 at 02:35:02PM -0500, Jason Baron wrote:
> As part of Jim Cromie's new dynamic debug classmap feature, the new code
> tries to toggle a jump label from dynamic_debug_setup(). However,
> dynamic_debug_setup() is called before the 'module_notify_list' notifier
> chain is invoked. And jump labels are initialized via the module notifier
> chain. Note this is an issue for a new feature not yet merged and doesn't
> affect any existing codepaths.

I think we can summarize this to "in preperation for some future work where
ordering matters with respect to jump labels" or something like that.

Because that is then making it specific to the future use case and
creates the current justification.

> We could just move dynamic_debug_setup() earlier in load_module(). But
> let's instead ensure the ordering via the 'priority' in the module list
> notifier.

"becuase the notifier for jump labels jump_label_module_nb uses a
priority of 1" or something like that would be nice to get added.

> This brings dynamic debug more in line with other subsystems and
> pulls code out of the core module code.

This should be the main reason for this change, as explained in the
commit log. A secondary benefit would be it fixes the first future bug
mentioned.

With those changes I can take this into modules-next to start getting
this tested sooner rather than later.

  Luis

Jason Baron Feb. 28, 2023, 9:56 p.m. UTC | #2

On 2/28/23 3:44 PM, Luis Chamberlain wrote:
> On Tue, Feb 28, 2023 at 02:35:02PM -0500, Jason Baron wrote:
>> As part of Jim Cromie's new dynamic debug classmap feature, the new code
>> tries to toggle a jump label from dynamic_debug_setup(). However,
>> dynamic_debug_setup() is called before the 'module_notify_list' notifier
>> chain is invoked. And jump labels are initialized via the module notifier
>> chain. Note this is an issue for a new feature not yet merged and doesn't
>> affect any existing codepaths.
> 
> I think we can summarize this to "in preperation for some future work where
> ordering matters with respect to jump labels" or something like that.
> 
> Because that is then making it specific to the future use case and
> creates the current justification.
> 
>> We could just move dynamic_debug_setup() earlier in load_module(). But
>> let's instead ensure the ordering via the 'priority' in the module list
>> notifier.
> 
> "becuase the notifier for jump labels jump_label_module_nb uses a
> priority of 1" or something like that would be nice to get added.
> 
>> This brings dynamic debug more in line with other subsystems and
>> pulls code out of the core module code.
> 
> This should be the main reason for this change, as explained in the
> commit log. A secondary benefit would be it fixes the first future bug
> mentioned.
> 
> With those changes I can take this into modules-next to start getting
> this tested sooner rather than later.
> 
>    Luis


Hi Luis,

Ok, I can fix up the commit message and re-post. I'm thinking maybe we 
should separate these patches as they are independent. The 2nd one I 
think makes sense to go through modules-next, but the first one is 
internal to dynamic debug and can be a part of Jim's series. Make sense?

Thanks,

-Jason

Luis Chamberlain Feb. 28, 2023, 11:34 p.m. UTC | #3

On Tue, Feb 28, 2023 at 04:56:59PM -0500, Jason Baron wrote:
> Ok, I can fix up the commit message and re-post. I'm thinking maybe we
> should separate these patches as they are independent. The 2nd one I think
> makes sense to go through modules-next, but the first one is internal to
> dynamic debug and can be a part of Jim's series. Make sense?

Sure but you may want to take a look at modules-next, does that patch
apply without any issues there? I have yet to rebase as v6.3-rc1 is not
out yet.

  Luis

Patch

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 41682278d2e8..f401414341fb 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -130,9 +130,6 @@  struct ddebug_class_param {
 
 #if defined(CONFIG_DYNAMIC_DEBUG_CORE)
 
-int ddebug_add_module(struct _ddebug_info *dyndbg, const char *modname);
-
-extern int ddebug_remove_module(const char *mod_name);
 extern __printf(2, 3)
 void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...);
 
@@ -304,16 +301,6 @@  int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp);
 #include <linux/errno.h>
 #include <linux/printk.h>
 
-static inline int ddebug_add_module(struct _ddebug_info *dinfo, const char *modname)
-{
-	return 0;
-}
-
-static inline int ddebug_remove_module(const char *mod)
-{
-	return 0;
-}
-
 static inline int ddebug_dyndbg_module_param_cb(char *param, char *val,
 						const char *modname)
 {
diff --git a/include/linux/module.h b/include/linux/module.h
index 8c5909c0076c..87d4ccc79445 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -27,6 +27,7 @@ 
 #include <linux/tracepoint-defs.h>
 #include <linux/srcu.h>
 #include <linux/static_call_types.h>
+#include <linux/dynamic_debug.h>
 
 #include <linux/percpu.h>
 #include <asm/module.h>
@@ -546,6 +547,9 @@  struct module {
 	struct error_injection_entry *ei_funcs;
 	unsigned int num_ei_funcs;
 #endif
+#ifdef CONFIG_DYNAMIC_DEBUG_CORE
+	struct _ddebug_info dyndbg_info;
+#endif
 } ____cacheline_aligned __randomize_layout;
 #ifndef MODULE_ARCH_INIT
 #define MODULE_ARCH_INIT {}
diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index 2e2bf236f558..7366fcf89103 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -53,7 +53,6 @@  extern const struct kernel_symbol __stop___ksymtab_gpl[];
 extern const s32 __start___kcrctab[];
 extern const s32 __start___kcrctab_gpl[];
 
-#include <linux/dynamic_debug.h>
 struct load_info {
 	const char *name;
 	/* pointer to module in temporary copy, freed at end of load_module() */
@@ -63,7 +62,6 @@  struct load_info {
 	Elf_Shdr *sechdrs;
 	char *secstrings, *strtab;
 	unsigned long symoffs, stroffs, init_typeoffs, core_typeoffs;
-	struct _ddebug_info dyndbg;
 	bool sig_ok;
 #ifdef CONFIG_KALLSYMS
 	unsigned long mod_kallsyms_init_off;
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 4ac3fe43e6c8..cd5e401e4dc3 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1157,9 +1157,6 @@  static void free_module(struct module *mod)
 	mod->state = MODULE_STATE_UNFORMED;
 	mutex_unlock(&module_mutex);
 
-	/* Remove dynamic debug info */
-	ddebug_remove_module(mod->name);
-
 	/* Arch-specific cleanup. */
 	module_arch_cleanup(mod);
 
@@ -1591,19 +1588,6 @@  static void free_modinfo(struct module *mod)
 	}
 }
 
-static void dynamic_debug_setup(struct module *mod, struct _ddebug_info *dyndbg)
-{
-	if (!dyndbg->num_descs)
-		return;
-	ddebug_add_module(dyndbg, mod->name);
-}
-
-static void dynamic_debug_remove(struct module *mod, struct _ddebug_info *dyndbg)
-{
-	if (dyndbg->num_descs)
-		ddebug_remove_module(mod->name);
-}
-
 void * __weak module_alloc(unsigned long size)
 {
 	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
@@ -2109,10 +2093,14 @@  static int find_module_sections(struct module *mod, struct load_info *info)
 	if (section_addr(info, "__obsparm"))
 		pr_warn("%s: Ignoring obsolete parameters\n", mod->name);
 
-	info->dyndbg.descs = section_objs(info, "__dyndbg",
-					sizeof(*info->dyndbg.descs), &info->dyndbg.num_descs);
-	info->dyndbg.classes = section_objs(info, "__dyndbg_classes",
-					sizeof(*info->dyndbg.classes), &info->dyndbg.num_classes);
+#ifdef CONFIG_DYNAMIC_DEBUG_CORE
+	mod->dyndbg_info.descs = section_objs(info, "__dyndbg",
+					      sizeof(*mod->dyndbg_info.descs),
+					      &mod->dyndbg_info.num_descs);
+	mod->dyndbg_info.classes = section_objs(info, "__dyndbg_classes",
+						sizeof(*mod->dyndbg_info.classes),
+						&mod->dyndbg_info.num_classes);
+#endif
 
 	return 0;
 }
@@ -2824,7 +2812,6 @@  static int load_module(struct load_info *info, const char __user *uargs,
 	}
 
 	init_build_id(mod, info);
-	dynamic_debug_setup(mod, &info->dyndbg);
 
 	/* Ftrace init must be called in the MODULE_STATE_UNFORMED state */
 	ftrace_module_init(mod);
@@ -2888,7 +2875,6 @@  static int load_module(struct load_info *info, const char __user *uargs,
 
  ddebug_cleanup:
 	ftrace_release_mod(mod);
-	dynamic_debug_remove(mod, &info->dyndbg);
 	synchronize_rcu();
 	kfree(mod->args);
  free_arch_cleanup:
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 8136e5236b7b..fdd6d9800a70 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -1223,7 +1223,7 @@  static void ddebug_attach_module_classes(struct ddebug_table *dt,
  * Allocate a new ddebug_table for the given module
  * and add it to the global list.
  */
-static int __ddebug_add_module(struct _ddebug_info *di, const char *modname)
+static int ddebug_add_module(struct _ddebug_info *di, const char *modname)
 {
 	struct ddebug_table *dt;
 
@@ -1262,11 +1262,6 @@  static int __ddebug_add_module(struct _ddebug_info *di, const char *modname)
 	return 0;
 }
 
-int ddebug_add_module(struct _ddebug_info *di, const char *modname)
-{
-	return __ddebug_add_module(di, modname);
-}
-
 /* helper for ddebug_dyndbg_(boot|module)_param_cb */
 static int ddebug_dyndbg_param_cb(char *param, char *val,
 				const char *modname, int on_err)
@@ -1313,11 +1308,13 @@  static void ddebug_table_free(struct ddebug_table *dt)
 	kfree(dt);
 }
 
+#ifdef CONFIG_MODULES
+
 /*
  * Called in response to a module being unloaded.  Removes
  * any ddebug_table's which point at the module.
  */
-int ddebug_remove_module(const char *mod_name)
+static int ddebug_remove_module(const char *mod_name)
 {
 	struct ddebug_table *dt, *nextdt;
 	int ret = -ENOENT;
@@ -1336,6 +1333,33 @@  int ddebug_remove_module(const char *mod_name)
 	return ret;
 }
 
+static int ddebug_module_notify(struct notifier_block *self, unsigned long val,
+				void *data)
+{
+	struct module *mod = data;
+	int ret = 0;
+
+	switch (val) {
+	case MODULE_STATE_COMING:
+		ret = ddebug_add_module(&mod->dyndbg_info, mod->name);
+		if (ret)
+			WARN(1, "Failed to allocate memory: dyndbg may not work properly.\n");
+		break;
+	case MODULE_STATE_GOING:
+		ddebug_remove_module(mod->name);
+		break;
+	}
+
+	return notifier_from_errno(ret);
+}
+
+static struct notifier_block ddebug_module_nb = {
+	.notifier_call = ddebug_module_notify,
+	.priority = 0, /* dynamic debug depends on jump label */
+};
+
+#endif /* CONFIG_MODULES */
+
 static void ddebug_remove_all_tables(void)
 {
 	mutex_lock(&ddebug_lock);
@@ -1387,6 +1411,14 @@  static int __init dynamic_debug_init(void)
 		.num_classes = __stop___dyndbg_classes - __start___dyndbg_classes,
 	};
 
+#ifdef CONFIG_MODULES
+	ret = register_module_notifier(&ddebug_module_nb);
+	if (ret) {
+		pr_warn("Failed to register dynamic debug module notifier\n");
+		return ret;
+	}
+#endif /* CONFIG_MODULES */
+
 	if (&__start___dyndbg == &__stop___dyndbg) {
 		if (IS_ENABLED(CONFIG_DYNAMIC_DEBUG)) {
 			pr_warn("_ddebug table is empty in a CONFIG_DYNAMIC_DEBUG build\n");
@@ -1407,7 +1439,7 @@  static int __init dynamic_debug_init(void)
 			mod_ct++;
 			di.num_descs = mod_sites;
 			di.descs = iter_mod_start;
-			ret = __ddebug_add_module(&di, modname);
+			ret = ddebug_add_module(&di, modname);
 			if (ret)
 				goto out_err;
 
@@ -1418,7 +1450,7 @@  static int __init dynamic_debug_init(void)
 	}
 	di.num_descs = mod_sites;
 	di.descs = iter_mod_start;
-	ret = __ddebug_add_module(&di, modname);
+	ret = ddebug_add_module(&di, modname);
 	if (ret)
 		goto out_err;