[ 3.5.y.z extended stable ] Patch "module: wait when loading a module which is currently" has been added to staging queue

[Herton Ronaldo Krzesinski]

This is a note to let you know that I have just added a patch titled

    module: wait when loading a module which is currently

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Herton

------

>From 4facfe4bb331890140d258836057eda40252371b Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty at rustcorp.com.au>
Date: Fri, 28 Sep 2012 14:31:03 +0930
Subject: [PATCH] module: wait when loading a module which is currently
 initializing.

commit 9bb9c3be56834653878f766f471fa1c20e562f4c upstream.

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 <lucas.demarchi at profusion.mobi>
Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 kernel/module.c |   28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 27e302a..8dd60f4 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2870,6 +2870,20 @@ static int post_relocation(struct module *mod, const struct load_info *info)
 	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,
@@ -2877,7 +2891,7 @@ static struct module *load_module(void __user *umod,
 				  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",
@@ -2943,8 +2957,18 @@ static struct module *load_module(void __user *umod,
 	 * 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;
 	}
--
1.7.9.5