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Subject: Re: [PATCH v4 1/3] kernel/notifier.c: intercepting duplicate
 registrations to avoid infinite loops
To:     Greg KH <gregkh@linuxfoundation.org>
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References: <1568861888-34045-1-git-send-email-nixiaoming@huawei.com>
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 <20190919063615.GA2069346@kroah.com>
From:   Xiaoming Ni <nixiaoming@huawei.com>
Message-ID: <b37575b1-2ea4-d813-c262-b52b322652c1@huawei.com>
Date:   Thu, 19 Sep 2019 20:55:19 +0800
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On 2019/9/19 14:36, Greg KH wrote:
> On Thu, Sep 19, 2019 at 10:58:06AM +0800, Xiaoming Ni wrote:
>> Registering the same notifier to a hook repeatedly can cause the hook
>> list to form a ring or lose other members of the list.
>>
>> case1: An infinite loop in notifier_chain_register() can cause soft lockup
>>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>>         atomic_notifier_chain_register(&test_notifier_list, &test2);
>>
>> case2: An infinite loop in notifier_chain_register() can cause soft lockup
>>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>>         atomic_notifier_call_chain(&test_notifier_list, 0, NULL);
>>
>> case3: lose other hook test2
>>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>>         atomic_notifier_chain_register(&test_notifier_list, &test2);
>>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>>
>> case4: Unregister returns 0, but the hook is still in the linked list,
>>         and it is not really registered. If you call notifier_call_chain
>>         after ko is unloaded, it will trigger oops.
>>
>> If the system is configured with softlockup_panic and the same
>> hook is repeatedly registered on the panic_notifier_list, it
>> will cause a loop panic.
>>
>> Add a check in notifier_chain_register(),
>> Intercepting duplicate registrations to avoid infinite loops
>>
>> Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
>> Reviewed-by: Vasily Averin <vvs@virtuozzo.com>
>> ---
>>  kernel/notifier.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> <formletter>
> 
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree.  Please read:
>     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> for how to do this properly.
> 
thanks for your guidance
I thought that as long as the code exists in the stable branch, it should be copied to stable@kernel.org
it is my mistake,

These patches are intended to be sent to the main line.
Should I resend it again?

> </formletter>
> 
> Same thing goes for all of the patches in this series.
> 
> thanks,
> 
> greg k-h
> 
> .
> 

thanks

Xiaoming Ni