From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756848Ab0FBCLU (ORCPT ); Tue, 1 Jun 2010 22:11:20 -0400 Received: from mail-pv0-f174.google.com ([74.125.83.174]:51683 "EHLO mail-pv0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755513Ab0FBCLT (ORCPT ); Tue, 1 Jun 2010 22:11:19 -0400 Date: Tue, 1 Jun 2010 19:10:29 -0700 From: Brandon Philips To: Linus Torvalds 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" Message-ID: <20100602021029.GD10332@jenkins.ifup.org> References: <201005252300.07739.rjw@sisk.pl> <201006011051.25636.rusty@rustcorp.com.au> <201006011452.06843.rusty@rustcorp.com.au> <20100601232430.GC10332@jenkins.ifup.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16:51 Tue 01 Jun 2010, Linus Torvalds wrote: > 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. Right. > > 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()). Right, I noticed that too and held the lock in the patch I sent. > 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!) FWIW, I tried this same idea initially and it breaks because the kobject EEXIST is coming from mod_sysfs_init() which happens further up in load_module() before the list_add_rcu(). I also tried the obvious variation of moving the list_add_rcu() up to where the find_module is but got: [ 5.495549] sd 0:0:1:0: [sda] 976773168 512-byte logical blocks: (500 GB/465 GiB) [ 5.496931] ehci_hcd: Unknown symbol usb_hcd_resume_root_hub (err 0) [ 5.497002] ehci_hcd: Unknown symbol usb_hcd_pci_probe (err 0) [ 5.497070] ehci_hcd: Unknown symbol usb_hcd_unlink_urb_from_ep (err 0) Feeling a bit like GoldiLocks I gave up and sent the modules_loading patch to illustrate the issue. :) I will keep working out all the interdependencies to see if I can get something to boot without something like the modules_loading list. Cheers, Brandon > 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);