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

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Date:   Thu, 11 Jul 2019 14:03:12 +0800
From:   Zhiqiang Liu <liuzhiqiang26@...wei.com>
To:     Jessica Yu <jeyu@...nel.org>
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



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 again.