Date:	Mon, 21 Jan 2013 12:12:21 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	Prarit Bhargava <prarit@...hat.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	stable@...r.kernel.org
Subject: Re: module: put modules in list much earlier.

Rusty, should the commit below be applied to the 3.7-stable kernel tree?

thanks,

greg k-h


On Mon, Jan 21, 2013 at 01:46:13AM +0000, Linux Kernel Mailing List wrote:
> Gitweb:     http://git.kernel.org/linus/;a=commit;h=1fb9341ac34825aa40354e74d9a2c69df7d2c304
> Commit:     1fb9341ac34825aa40354e74d9a2c69df7d2c304
> Parent:     0d21b0e3477395e7ff2acc269f15df6e6a8d356d
> Author:     Rusty Russell <rusty@...tcorp.com.au>
> AuthorDate: Sat Jan 12 13:27:34 2013 +1030
> Committer:  Rusty Russell <rusty@...tcorp.com.au>
> CommitDate: Sat Jan 12 13:27:46 2013 +1030
> 
>     module: put modules in list much earlier.
>     
>     Prarit's excellent bug report:
>     > In recent Fedora releases (F17 & F18) some users have reported seeing
>     > messages similar to
>     >
>     > [   15.478160] kvm: Could not allocate 304 bytes percpu data
>     > [   15.478174] PERCPU: allocation failed, size=304 align=32, alloc from
>     > reserved chunk failed
>     >
>     > during system boot.  In some cases, users have also reported seeing this
>     > message along with a failed load of other modules.
>     >
>     > What is happening is systemd is loading an instance of the kvm module for
>     > each cpu found (see commit e9bda3b).  When the module load occurs the kernel
>     > currently allocates the modules percpu data area prior to checking to see
>     > if the module is already loaded or is in the process of being loaded.  If
>     > the module is already loaded, or finishes load, the module loading code
>     > releases the current instance's module's percpu data.
>     
>     Now we have a new state MODULE_STATE_UNFORMED, we can insert the
>     module into the list (and thus guarantee its uniqueness) before we
>     allocate the per-cpu region.
>     
>     Reported-by: Prarit Bhargava <prarit@...hat.com>
>     Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
>     Tested-by: Prarit Bhargava <prarit@...hat.com>
> ---
>  kernel/module.c |   90 ++++++++++++++++++++++++++++++-------------------------
>  lib/bug.c       |    1 +
>  2 files changed, 50 insertions(+), 41 deletions(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index c3a2ee8..ec535aa 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3017,7 +3017,7 @@ static bool finished_loading(const char *name)
>  	bool ret;
>  
>  	mutex_lock(&module_mutex);
> -	mod = find_module(name);
> +	mod = find_module_all(name, true);
>  	ret = !mod || mod->state == MODULE_STATE_LIVE
>  		|| mod->state == MODULE_STATE_GOING;
>  	mutex_unlock(&module_mutex);
> @@ -3141,6 +3141,32 @@ static int load_module(struct load_info *info, const char __user *uargs,
>  		goto free_copy;
>  	}
>  
> +	/*
> +	 * We try to place it in the list now to make sure it's unique
> +	 * before we dedicate too many resources.  In particular,
> +	 * temporary percpu memory exhaustion.
> +	 */
> +	mod->state = MODULE_STATE_UNFORMED;
> +again:
> +	mutex_lock(&module_mutex);
> +	if ((old = find_module_all(mod->name, true)) != NULL) {
> +		if (old->state == MODULE_STATE_COMING
> +		    || old->state == MODULE_STATE_UNFORMED) {
> +			/* Wait in case it fails to load. */
> +			mutex_unlock(&module_mutex);
> +			err = wait_event_interruptible(module_wq,
> +					       finished_loading(mod->name));
> +			if (err)
> +				goto free_module;
> +			goto again;
> +		}
> +		err = -EEXIST;
> +		mutex_unlock(&module_mutex);
> +		goto free_module;
> +	}
> +	list_add_rcu(&mod->list, &modules);
> +	mutex_unlock(&module_mutex);
> +
>  #ifdef CONFIG_MODULE_SIG
>  	mod->sig_ok = info->sig_ok;
>  	if (!mod->sig_ok)
> @@ -3150,7 +3176,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
>  	/* Now module is in final location, initialize linked lists, etc. */
>  	err = module_unload_init(mod);
>  	if (err)
> -		goto free_module;
> +		goto unlink_mod;
>  
>  	/* Now we've got everything in the final locations, we can
>  	 * find optional sections. */
> @@ -3185,54 +3211,33 @@ static int load_module(struct load_info *info, const char __user *uargs,
>  		goto free_arch_cleanup;
>  	}
>  
> -	/* Mark state as coming so strong_try_module_get() ignores us. */
> -	mod->state = MODULE_STATE_COMING;
> -
> -	/* Now sew it into the lists so we can get lockdep and oops
> -	 * info during argument parsing.  No one should access us, since
> -	 * strong_try_module_get() will fail.
> -	 * lockdep/oops can run asynchronous, so use the RCU list insertion
> -	 * function to insert in a way safe to concurrent readers.
> -	 * The mutex protects against concurrent writers.
> -	 */
> -again:
> -	mutex_lock(&module_mutex);
> -	if ((old = find_module(mod->name)) != NULL) {
> -		if (old->state == MODULE_STATE_COMING) {
> -			/* Wait in case it fails to load. */
> -			mutex_unlock(&module_mutex);
> -			err = wait_event_interruptible(module_wq,
> -					       finished_loading(mod->name));
> -			if (err)
> -				goto free_arch_cleanup;
> -			goto again;
> -		}
> -		err = -EEXIST;
> -		goto unlock;
> -	}
> -
> -	/* This has to be done once we're sure module name is unique. */
>  	dynamic_debug_setup(info->debug, info->num_debug);
>  
> -	/* Find duplicate symbols */
> +	mutex_lock(&module_mutex);
> +	/* Find duplicate symbols (must be called under lock). */
>  	err = verify_export_symbols(mod);
>  	if (err < 0)
> -		goto ddebug;
> +		goto ddebug_cleanup;
>  
> +	/* This relies on module_mutex for list integrity. */
>  	module_bug_finalize(info->hdr, info->sechdrs, mod);
> -	list_add_rcu(&mod->list, &modules);
> +
> +	/* Mark state as coming so strong_try_module_get() ignores us,
> +	 * but kallsyms etc. can see us. */
> +	mod->state = MODULE_STATE_COMING;
> +
>  	mutex_unlock(&module_mutex);
>  
>  	/* Module is ready to execute: parsing args may do that. */
>  	err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
>  			 -32768, 32767, &ddebug_dyndbg_module_param_cb);
>  	if (err < 0)
> -		goto unlink;
> +		goto bug_cleanup;
>  
>  	/* Link in to syfs. */
>  	err = mod_sysfs_setup(mod, info, mod->kp, mod->num_kp);
>  	if (err < 0)
> -		goto unlink;
> +		goto bug_cleanup;
>  
>  	/* Get rid of temporary copy. */
>  	free_copy(info);
> @@ -3242,16 +3247,13 @@ again:
>  
>  	return do_init_module(mod);
>  
> - unlink:
> + bug_cleanup:
> +	/* module_bug_cleanup needs module_mutex protection */
>  	mutex_lock(&module_mutex);
> -	/* Unlink carefully: kallsyms could be walking list. */
> -	list_del_rcu(&mod->list);
>  	module_bug_cleanup(mod);
> -	wake_up_all(&module_wq);
> - ddebug:
> -	dynamic_debug_remove(info->debug);
> - unlock:
>  	mutex_unlock(&module_mutex);
> + ddebug_cleanup:
> +	dynamic_debug_remove(info->debug);
>  	synchronize_sched();
>  	kfree(mod->args);
>   free_arch_cleanup:
> @@ -3260,6 +3262,12 @@ again:
>  	free_modinfo(mod);
>   free_unload:
>  	module_unload_free(mod);
> + unlink_mod:
> +	mutex_lock(&module_mutex);
> +	/* Unlink carefully: kallsyms could be walking list. */
> +	list_del_rcu(&mod->list);
> +	wake_up_all(&module_wq);
> +	mutex_unlock(&module_mutex);
>   free_module:
>  	module_deallocate(mod, info);
>   free_copy:
> diff --git a/lib/bug.c b/lib/bug.c
> index a28c141..d0cdf14 100644
> --- a/lib/bug.c
> +++ b/lib/bug.c
> @@ -55,6 +55,7 @@ static inline unsigned long bug_addr(const struct bug_entry *bug)
>  }
>  
>  #ifdef CONFIG_MODULES
> +/* Updates are protected by module mutex */
>  static LIST_HEAD(module_bug_list);
>  
>  static const struct bug_entry *module_find_bug(unsigned long bugaddr)
> --
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