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Date: Tue, 1 Jun 2010 16:51:43 -0700 (PDT) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Brandon Philips <brandon@...p.org> cc: Rusty Russell <rusty@...tcorp.com.au>, Andrew Morton <akpm@...ux-foundation.org>, "Rafael J. Wysocki" <rjw@...k.pl>, LKML <linux-kernel@...r.kernel.org>, Jon Masters <jonathan@...masters.org>, Tejun Heo <htejun@...il.com>, Masami Hiramatsu <mhiramat@...hat.com>, Kay Sievers <kay.sievers@...y.org> Subject: Re: [PATCH 2/2] module: fix bne2 "gave up waiting for init of module libcrc32c" 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@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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