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

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Date:   Mon, 1 Jan 2018 22:40:36 +0530
From:   Pravin Shedge <pravin.shedge4linux@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Davidlohr Bueso <dave@...olabs.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] lib: Remove module auto-unloading which encourages
 inconsistent behaviour

On Fri, Dec 29, 2017 at 10:17 PM, Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Sat, Dec 23, 2017 at 5:28 PM, Pravin Shedge
> <pravin.shedge4linux@...il.com> wrote:
>> 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.
>>
>
> Suggested-by: Andrew ... ?
Hi Andy,

Please check the reference patch "[PATCH] lib: add module unload
support to sort tests" this patch was added for lib/test_sort.c file.
test_sort.c missing unloading feature so I added auto-unload feature
for the same. But after reviewers comment I am agree on the part that
module auto-unload feature will break the consistency from users point
of view.

The reviewers for this patch are Andrew, Paul Gortmaker.

Thanks & Regards,
  PraviN



>
>> 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
>>
>
>
>
> --
> With Best Regards,
> Andy Shevchenko