Re: [PATCH v9 13/14] module: Move kdb_modules list out of core code

[Luis Chamberlain <mcgrof@kernel.org>]

On Thu, Mar 03, 2022 at 09:54:14AM -0800, Christoph Hellwig wrote:
> On Thu, Mar 03, 2022 at 02:59:49PM +0000, Daniel Thompson wrote:
> > 
> > One of the best ways that we can common up code might be to dust
> > off some code I wrote a while back to display seq_files from
> > kdb.
> > 
> > The basic idea worked well enough but it often needs special
> > start/stop operatings to ensure the start meeds kdb's rather
> > odd locking restrictions. If there is a willingness for
> > something like the below to be included in the module code then we
> > could replace kdb_lsmod() with something that reused the code to
> >  format /proc/modules.
> 
> Displaying seq_files sounds nice to have, but in the short term I'm
> just thinking of something like this:
> 
> diff --git a/include/linux/kdb.h b/include/linux/kdb.h
> index ea0f5e580fac2..07dfb6a20a1c4 100644
> --- a/include/linux/kdb.h
> +++ b/include/linux/kdb.h
> @@ -222,5 +222,6 @@ enum {
>  
>  extern int kdbgetintenv(const char *, int *);
>  extern int kdb_set(int, const char **);
> +int kdb_lsmod(int argc, const char **argv);

Yes exactly.

>  #endif	/* !_KDB_H */
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index 0852a537dad4c..292a407118a4f 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -2004,54 +2004,6 @@ static int kdb_ef(int argc, const char **argv)
>  	return 0;
>  }
>  
> -#if defined(CONFIG_MODULES)
> -/*
> - * kdb_lsmod - This function implements the 'lsmod' command.  Lists
> - *	currently loaded kernel modules.
> - *	Mostly taken from userland lsmod.
> - */
> -static int kdb_lsmod(int argc, const char **argv)
> -{
> -	struct module *mod;
> -
> -	if (argc != 0)
> -		return KDB_ARGCOUNT;
> -
> -	kdb_printf("Module                  Size  modstruct     Used by\n");
> -	list_for_each_entry(mod, kdb_modules, list) {
> -		if (mod->state == MODULE_STATE_UNFORMED)
> -			continue;
> -
> -		kdb_printf("%-20s%8u  0x%px ", mod->name,
> -			   mod->core_layout.size, (void *)mod);
> -#ifdef CONFIG_MODULE_UNLOAD
> -		kdb_printf("%4d ", module_refcount(mod));
> -#endif
> -		if (mod->state == MODULE_STATE_GOING)
> -			kdb_printf(" (Unloading)");
> -		else if (mod->state == MODULE_STATE_COMING)
> -			kdb_printf(" (Loading)");
> -		else
> -			kdb_printf(" (Live)");
> -		kdb_printf(" 0x%px", mod->core_layout.base);
> -
> -#ifdef CONFIG_MODULE_UNLOAD
> -		{
> -			struct module_use *use;
> -			kdb_printf(" [ ");
> -			list_for_each_entry(use, &mod->source_list,
> -					    source_list)
> -				kdb_printf("%s ", use->target->name);
> -			kdb_printf("]\n");
> -		}
> -#endif
> -	}
> -
> -	return 0;
> -}
> -
> -#endif	/* CONFIG_MODULES */
> -
>  /*
>   * kdb_env - This function implements the 'env' command.  Display the
>   *	current environment variables.
> diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
> index 0d2f9feea0a46..1f8c519a5f81c 100644
> --- a/kernel/debug/kdb/kdb_private.h
> +++ b/kernel/debug/kdb/kdb_private.h
> @@ -226,10 +226,6 @@ extern void kdb_kbd_cleanup_state(void);
>  #define kdb_kbd_cleanup_state()
>  #endif /* ! CONFIG_KDB_KEYBOARD */
>  
> -#ifdef CONFIG_MODULES
> -extern struct list_head *kdb_modules;
> -#endif /* CONFIG_MODULES */
> -
>  extern char kdb_prompt_str[];
>  
>  #define	KDB_WORD_SIZE	((int)sizeof(unsigned long))
> diff --git a/kernel/module.c b/kernel/module.c
> index 6cea788fd965c..754ec20aab4f1 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -57,6 +57,7 @@
>  #include <linux/bsearch.h>
>  #include <linux/dynamic_debug.h>
>  #include <linux/audit.h>
> +#include <linux/kdb.h>
>  #include <uapi/linux/module.h>
>  #include "module-internal.h"
>  
> @@ -252,10 +253,6 @@ static void mod_update_bounds(struct module *mod)
>  		__mod_update_bounds(mod->init_layout.base, mod->init_layout.size);
>  }
>  
> -#ifdef CONFIG_KGDB_KDB
> -struct list_head *kdb_modules = &modules; /* kdb needs the list of modules */
> -#endif /* CONFIG_KGDB_KDB */
> -
>  static void module_assert_mutex_or_preempt(void)
>  {
>  #ifdef CONFIG_LOCKDEP
> @@ -4808,3 +4805,45 @@ void module_layout(struct module *mod,
>  }
>  EXPORT_SYMBOL(module_layout);
>  #endif
> +
> +#ifdef CONFIG_KGDB_KDB

Yes! And then when we move all this crap to its own files on
kernel/module/Makefile:

obj-$(CONFIG_KGDB_KDB) += kdb.o

> +int kdb_lsmod(int argc, const char **argv)
> +{
> +	struct module *mod;
> +
> +	if (argc != 0)
> +		return KDB_ARGCOUNT;
> +
> +	kdb_printf("Module                  Size  modstruct     Used by\n");

Indeed, we need to do it this way because kdb_printf() which emits
messages directly to I/O drivers, bypassing the kernel log. Perhaps this
info should be added to the top of kernel/module/kdb.c

> +	list_for_each_entry(mod, &modules, list) {
> +		if (mod->state == MODULE_STATE_UNFORMED)
> +			continue;
> +
> +		kdb_printf("%-20s%8u  0x%px ", mod->name,
> +			   mod->core_layout.size, (void *)mod);
> +#ifdef CONFIG_MODULE_UNLOAD
> +		kdb_printf("%4d ", module_refcount(mod));
> +#endif

Yes and later this can be if IS_ENABLED(CONFIG_MODULE_UNLOAD)

> +		if (mod->state == MODULE_STATE_GOING)
> +			kdb_printf(" (Unloading)");
> +		else if (mod->state == MODULE_STATE_COMING)
> +			kdb_printf(" (Loading)");
> +		else
> +			kdb_printf(" (Live)");
> +		kdb_printf(" 0x%px", mod->core_layout.base);
> +
> +#ifdef CONFIG_MODULE_UNLOAD

and if IS_ENABLED(CONFIG_MODULE_UNLOAD) later

> +		{
> +			struct module_use *use;
> +			kdb_printf(" [ ");
> +			list_for_each_entry(use, &mod->source_list,
> +					    source_list)
> +				kdb_printf("%s ", use->target->name);
> +			kdb_printf("]\n");
> +		}
> +#endif
> +	}
> +
> +	return 0;
> +}
> +#endif	/* CONFIG_KGDB_KDB */

  Luis