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Subject: Re: [PATCH v2] module: add usage links when calling ref_module func
To:     Jessica Yu <jeyu@kernel.org>
CC:     <rusty@rustcorp.com.au>, <kay.sievers@vrfy.org>,
        <clabbe.montjoie@gmail.com>, LKML <linux-kernel@vger.kernel.org>,
        <wangxiaogang3@huawei.com>, <zhoukang7@huawei.com>,
        Mingfangsen <mingfangsen@huawei.com>
References: <4fec6c3b-03b8-dd57-4009-99431105a8a5@huawei.com>
 <20190709161039.GA3501@linux-8ccs>
From:   Zhiqiang Liu <liuzhiqiang26@huawei.com>
Message-ID: <de919fd8-afd8-244c-d316-19d5a3895406@huawei.com>
Date:   Thu, 11 Jul 2019 14:03:12 +0800
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On 2019/7/10 0:10, Jessica Yu wrote:
> +++ Zhiqiang Liu [03/07/19 10:09 +0800]:
>> From: Zhiqiang Liu <liuzhiqiang26@huawei.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@huawei.com>
>> Suggested-by: Jessica Yu <jeyu@kernel.org>
>> Reviewed-by: Kang Zhou <zhoukang7@huawei.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)
>> ?0?2*?0?2?0?2?0?2 'b' can walk the list to see who sourced them), and of 'a'
>> ?0?2*?0?2?0?2?0?2 targets (so 'a' can see what modules it targets).
>> ?0?2*/
>> /* Module a uses b: caller needs module_mutex() */
>> int ref_module(struct module *a, struct module *b)
>> {
>> +?0?2?0?2?0?2 struct module_use *use;
>> ?0?2?0?2?0?2?0?2int err;
>>
>> ?0?2?0?2?0?2?0?2if (b == NULL || already_uses(a, b))
>> @@ -866,9 +867,18 @@ int ref_module(struct module *a, struct module *b)
>> ?0?2?0?2?0?2?0?2if (err)
>> ?0?2?0?2?0?2?0?2?0?2?0?2?0?2 return err;
>>
>> -?0?2?0?2?0?2 err = add_module_usage(a, b);
>> +?0?2?0?2?0?2 use = add_module_usage(a, b);
>> +?0?2?0?2?0?2 if (!use) {
>> +?0?2?0?2?0?2?0?2?0?2?0?2?0?2 module_put(b);
>> +?0?2?0?2?0?2?0?2?0?2?0?2?0?2 return -ENOMEM;
>> +?0?2?0?2?0?2 }
>> +
>> +?0?2?0?2?0?2 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.