linux-kernel - [PATCH 2/2] lib: Remove module auto-unloading which encourages inconsistent behaviour

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Date:   Sat, 23 Dec 2017 20:58:49 +0530
From:   Pravin Shedge <pravin.shedge4linux@...il.com>
To:     dave@...olabs.net, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Cc:     pravin.shedge4linux@...il.com
Subject: [PATCH 2/2] lib: Remove module auto-unloading which encourages inconsistent behaviour

The module auto-unload might seem like a nice optimization, but
it encourages inconsistent behaviour. And behaviour that is
different from all other normal modules.

rbtree_test.c and percpu_test.c returns -EAGAIN from module_init()
on successful completion. Normal module return 0 on success but
returning -EAGAIN perform auto module unloading which seem like
a nice optimization but it brings inconsistent behaviour as well.

I face the similar problem in my previous patch, "Paul Gortmaker"
gives nice review comment on module auto-unloading brings
inconsistent behaviour.

Imagine something as simple as this:

        for i in $LIST ; do
                modprobe $i
                lsmod | grep -q $i
                if [ $? != 0 ]; then echo Module $i is not present! ; fi
        done

OK, not ideal code, ignoring the modprobe return -- but what it reports
is true --
rbtree_test.c and percpu_test.c test module (if it passed) will NOT be
present.

All other modules from linux/lib/* follow the same semantics that
module_init() returns 0 on successful completion & let external entity
like rmmod do the module unloading task.

Signed-off-by: Pravin Shedge <pravin.shedge4linux@...il.com>
---
 lib/percpu_test.c | 3 ++-
 lib/rbtree_test.c | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/lib/percpu_test.c b/lib/percpu_test.c
index 0b5d14d..57a637b 100644
--- a/lib/percpu_test.c
+++ b/lib/percpu_test.c
@@ -123,7 +123,8 @@ static int __init percpu_test_init(void)
 	preempt_enable();

 	pr_info("percpu test done\n");
-	return -EAGAIN;  /* Fail will directly unload the module */
+
+	return 0;
 }

 static void __exit percpu_test_exit(void)
diff --git a/lib/rbtree_test.c b/lib/rbtree_test.c
index 7d36c1e..5c52112 100644
--- a/lib/rbtree_test.c
+++ b/lib/rbtree_test.c
@@ -394,7 +394,7 @@ static int __init rbtree_test_init(void)

 	kfree(nodes);

-	return -EAGAIN; /* Fail will directly unload the module */
+	return 0;
 }

 static void __exit rbtree_test_exit(void)
-- 
2.7.4