linux-kernel - Re: [PATCH v2] module: add usage links when calling ref

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Date:   Thu, 11 Jul 2019 11:17:23 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Zhiqiang Liu <liuzhiqiang26@...wei.com>
Cc:     rusty@...tcorp.com.au, kay.sievers@...y.org,
        clabbe.montjoie@...il.com, LKML <linux-kernel@...r.kernel.org>,
        wangxiaogang3@...wei.com, zhoukang7@...wei.com,
        Mingfangsen <mingfangsen@...wei.com>
Subject: Re: [PATCH v2] module: add usage links when calling ref_module func

+++ Zhiqiang Liu [11/07/19 14:03 +0800]:
>
>
>On 2019/7/10 0:10, Jessica Yu wrote:
>> +++ Zhiqiang Liu [03/07/19 10:09 +0800]:
>>> From: Zhiqiang Liu <liuzhiqiang26@...wei.com
>>>
>>> V1->V2:
>>> - remove incorrect Fixes tag
>>> - fix error handling of sysfs_create_link as suggested by Jessica Yu
>>>
>>> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@...wei.com>
>>> Suggested-by: Jessica Yu <jeyu@...nel.org>
>>> Reviewed-by: Kang Zhou <zhoukang7@...wei.com>
>>> ---
>>> kernel/module.c | 18 ++++++++++++++----
>>> 1 file changed, 14 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/kernel/module.c b/kernel/module.c
>>> index 80c7c09584cf..672abce2222c 100644
>>> --- a/kernel/module.c
>>> +++ b/kernel/module.c
>>> @@ -837,25 +837,26 @@ static int already_uses(struct module *a, struct module *b)
>>>  *    'b' can walk the list to see who sourced them), and of 'a'
>>>  *    targets (so 'a' can see what modules it targets).
>>>  */
>>> /* Module a uses b: caller needs module_mutex() */
>>> int ref_module(struct module *a, struct module *b)
>>> {
>>> +    struct module_use *use;
>>>     int err;
>>>
>>>     if (b == NULL || already_uses(a, b))
>>> @@ -866,9 +867,18 @@ int ref_module(struct module *a, struct module *b)
>>>     if (err)
>>>         return err;
>>>
>>> -    err = add_module_usage(a, b);
>>> +    use = add_module_usage(a, b);
>>> +    if (!use) {
>>> +        module_put(b);
>>> +        return -ENOMEM;
>>> +    }
>>> +
>>> +    err = sysfs_create_link(b->holders_dir, &a->mkobj.kobj, a->name);
>>
>> Sigh. This ultimately doesn't work because in load_module(), we use
>> ref_module() in resolve_symbol(), and mod->mkobj.kobj doesn't get
>> initialized until mod_sysfs_init(), which happens much later in
>> load_module(). So what happens is that the ref_module(mod, owner) call
>> in resolve_symbol() returns an error because sysfs_create_link() fails here.
>> We could *maybe* move sysfs initialization earlier in load_module()
>> but that is an entirely untested idea and I would need to think about
>> that more.
>
>Thank you for the reply.
>I have tested the patch through livepatch. Maybe I miss somethings.
>I will rewrite the patch and test it entirely before sending the v3 patch.

Thanks Zhiqiang. A boot test and testing loading modules with
dependencies would be really appreciated.

Thanks!

Jessica