From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756263Ab2INHMa (ORCPT ); Fri, 14 Sep 2012 03:12:30 -0400 Received: from ozlabs.org ([203.10.76.45]:51443 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755983Ab2INHM1 (ORCPT ); Fri, 14 Sep 2012 03:12:27 -0400 From: Rusty Russell To: LKML Cc: Lucas De Marchi , Jon Masters Subject: [PATCH 2/2] module: wait when loading a module which is currently initializing. In-Reply-To: <87obl9rsg2.fsf@rustcorp.com.au> References: <87obl9rsg2.fsf@rustcorp.com.au> User-Agent: Notmuch/0.13.2 (http://notmuchmail.org) Emacs/23.3.1 (i686-pc-linux-gnu) Date: Fri, 14 Sep 2012 16:41:52 +0930 Message-ID: <87ligdrscn.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The original module-init-tools module loader used a fnctl lock on the .ko file to avoid attempts to simultaneously load a module. Unfortunately, you can't get an exclusive fcntl lock on a read-only fd, making this not work for read-only mounted filesystems. module-init-tools has a hacky sleep-and-loop for this now. It's not that hard to wait in the kernel, and only return -EEXIST once the first module has finished loading (or continue loading the module if the first one failed to initialize for some reason). It's also consistent with what we do for dependent modules which are still loading. Suggested-by: Lucas De Marchi Signed-off-by: Rusty Russell --- kernel/module.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) diff --git a/kernel/module.c b/kernel/module.c --- a/kernel/module.c +++ b/kernel/module.c @@ -2845,6 +2845,20 @@ static int post_relocation(struct module return module_finalize(info->hdr, info->sechdrs, mod); } +/* Is this module of this name done loading? No locks held. */ +static bool finished_loading(const char *name) +{ + struct module *mod; + bool ret; + + mutex_lock(&module_mutex); + mod = find_module(name); + ret = !mod || mod->state != MODULE_STATE_COMING; + mutex_unlock(&module_mutex); + + return ret; +} + /* Allocate and load the module: note that size of section 0 is always zero, and we rely on this for optional sections. */ static struct module *load_module(void __user *umod, @@ -2852,7 +2866,7 @@ static struct module *load_module(void _ const char __user *uargs) { struct load_info info = { NULL, }; - struct module *mod; + struct module *mod, *old; long err; pr_debug("load_module: umod=%p, len=%lu, uargs=%p\n", @@ -2918,8 +2932,18 @@ static struct module *load_module(void _ * function to insert in a way safe to concurrent readers. * The mutex protects against concurrent writers. */ +again: mutex_lock(&module_mutex); - if (find_module(mod->name)) { + 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; }