Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754981Ab0FAX4f (ORCPT ); Tue, 1 Jun 2010 19:56:35 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:48298 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751635Ab0FAX4e (ORCPT ); Tue, 1 Jun 2010 19:56:34 -0400 Date: Tue, 1 Jun 2010 16:51:43 -0700 (PDT) From: Linus Torvalds To: Brandon Philips cc: Rusty Russell , Andrew Morton , "Rafael J. Wysocki" , LKML , Jon Masters , Tejun Heo , Masami Hiramatsu , Kay Sievers Subject: Re: [PATCH 2/2] module: fix bne2 "gave up waiting for init of module libcrc32c" In-Reply-To: <20100601232430.GC10332@jenkins.ifup.org> Message-ID: References: <201005252300.07739.rjw@sisk.pl> <201006011051.25636.rusty@rustcorp.com.au> <201006011452.06843.rusty@rustcorp.com.au> <20100601232430.GC10332@jenkins.ifup.org> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) 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 Content-Length: 2693 Lines: 80 On Tue, 1 Jun 2010, Brandon Philips wrote: > > When I tested a Kernel with Rusty's modules branch pulled onto > 2.6.35-rc1 I got duplicate sysfs path errors: Hmm. Yeah, the module_mutex used to be held across the whole "find -> add" state, but isn't any more. > To fix this we need to make sure that we only have one copy of a module > going through load_module at a time. Patch suggestion follows which > boots without errors. I am sure there is a better way to do what it does > ;) I think Rusty may have made the lock a bit _too_ finegrained there, and didn't add it to some places that needed it. It looks, for example, like PATCH 1/2 actually drops the lock in places where it's needed ("find_module()" is documented to need it, but now load_module() didn't hold it at all when it did the find_module()). Rather than adding a new "module_loading" list, I think we should be able to just use the existing "modules" list, and just fix up the locking a bit. In fact, maybe we could just move the "look up existing module" a bit later - optimistically assuming that the module doesn't exist, and then just undoing the work if it turns out that we were wrong, just before adding ourselves to the list. A patch something like the appended (TOTALLY UNTESTED!) Linus --- kernel/module.c | 13 ++++++++----- 1 files changed, 8 insertions(+), 5 deletions(-) diff --git a/kernel/module.c b/kernel/module.c index a1f46a5..21f7ffa 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -2198,11 +2198,6 @@ static noinline struct module *load_module(void __user *umod, goto free_mod; } - if (find_module(mod->name)) { - err = -EEXIST; - goto free_mod; - } - mod->state = MODULE_STATE_COMING; /* Allow arches to frob section contents and sizes. */ @@ -2486,6 +2481,13 @@ static noinline struct module *load_module(void __user *umod, * The mutex protects against concurrent writers. */ mutex_lock(&module_mutex); + + if (find_module(mod->name)) { + err = -EEXIST; + /* This will also unlock the mutex */ + goto already_exists; + } + list_add_rcu(&mod->list, &modules); mutex_unlock(&module_mutex); @@ -2511,6 +2513,7 @@ static noinline struct module *load_module(void __user *umod, mutex_lock(&module_mutex); /* Unlink carefully: kallsyms could be walking list. */ list_del_rcu(&mod->list); + already_exists: mutex_unlock(&module_mutex); synchronize_sched(); module_arch_cleanup(mod); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/