linux-kernel - Re: [PATCH] Remove extra unlock for the mutex

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Message-ID: <3073e9a6-9f10-4326-9734-7e203d509888@gmail.com>
Date:   Wed, 11 Oct 2023 21:19:51 +0530
From:   Abhinav Singh <singhabhinav9051571833@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     davem@...emloft.net, dsahern@...nel.org, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Remove extra unlock for the mutex

On 10/11/23 12:00, Greg KH wrote:
> On Wed, Oct 11, 2023 at 04:16:30AM +0530, Abhinav Singh wrote:
>> There is a double unlock on mutex. This can cause undefined behaviour.
>>
>> Signed-off-by: Abhinav Singh <singhabhinav9051571833@...il.com>
>> ---
>>   net/ipv4/inet_connection_sock.c | 1 -
>>   1 file changed, 1 deletion(-)
>>
>> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
>> index aeebe8816689..f11fe8c727a4 100644
>> --- a/net/ipv4/inet_connection_sock.c
>> +++ b/net/ipv4/inet_connection_sock.c
>> @@ -597,7 +597,6 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum)
>>   	}
>>   	if (head2_lock_acquired)
>>   		spin_unlock(&head2->lock);
>> -	spin_unlock_bh(&head->lock);
> 
> How was this tested?
> 
> And where is the now-needed unlock of the head->lock?
> 
> How was this change found?
> 
> And your subject line needs a lot of work...
> 
> thanks,
> 
> greg k-h
Hello, I used sparse tool and got it this warning message "warning: 
context imbalance in 'inet_csk_get_port' - unexpected unlock"
Due to my over excitement of sending a good patch to kernel I didnt see 
correctly and misread `head` as `head2` and thought it was double 
unlocking the mutex. I m very sorry. But on a different note think we 
should do a check for `head->lock` as well before unlocking. Unlocking a 
non locked mutex can also trigger a undefined behaviour.

Thank you,
Abhinav Singh