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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Luiz Augusto von Dentz <luiz.dentz@gmail.com>, Lin Ma <linma@zju.edu.cn>
Cc: Marcel Holtmann <marcel@holtmann.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	"linux-bluetooth@vger.kernel.org"
	<linux-bluetooth@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	"open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>
Subject: Re: [PATCH v2] Bluetooth: call lock_sock() outside of spinlock section
Date: Sat, 10 Jul 2021 22:34:29 +0900	[thread overview]
Message-ID: <9771b40f-b544-a2a7-04e1-eddb38a4aae7@i-love.sakura.ne.jp> (raw)
In-Reply-To: <79694c01-b69e-a039-6860-d7e612fbc008@i-love.sakura.ne.jp>

On 2021/07/08 8:33, Tetsuo Handa wrote:
>>              we could perhaps don't release the reference to hdev
>> either and leave hci_sock_release to deal with it and then perhaps we
>> can take away the backward goto, actually why are you restarting to
>> begin with?
> 
> Do you mean something like
> 
> diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
> index b04a5a02ecf3..0525883f4639 100644
> --- a/net/bluetooth/hci_sock.c
> +++ b/net/bluetooth/hci_sock.c
> @@ -759,19 +759,14 @@ void hci_sock_dev_event(struct hci_dev *hdev, int event)
>  	if (event == HCI_DEV_UNREG) {
>  		struct sock *sk;
>  
> -		/* Detach sockets from device */
> +		/* Change socket state and notify */
>  		read_lock(&hci_sk_list.lock);
>  		sk_for_each(sk, &hci_sk_list.head) {
> -			lock_sock(sk);
>  			if (hci_pi(sk)->hdev == hdev) {
> -				hci_pi(sk)->hdev = NULL;
>  				sk->sk_err = EPIPE;
>  				sk->sk_state = BT_OPEN;
>  				sk->sk_state_change(sk);
> -
> -				hci_dev_put(hdev);
>  			}
> -			release_sock(sk);
>  		}
>  		read_unlock(&hci_sk_list.lock);
>  	}
> 
> ? I can't judge because I don't know how this works. I worry that
> without lock_sock()/release_sock(), this races with e.g. hci_sock_bind().
> 

I examined hci_unregister_dev() and concluded that this can't work.

hci_sock_dev_event(hdev, HCI_DEV_UNREG) can't defer dropping the reference to
this hdev till hci_sock_release(), for hci_unregister_dev() cleans up everything
related to this hdev and calls hci_dev_put(hdev) and then vhci_release() calls
hci_free_dev(hdev).

That's the reason hci_sock_dev_event() has to use lock_sock() in order not to
miss some hci_dev_put(hdev) calls.

>> This sounds a little too complicated, afaik backward goto is not even
>> consider a good practice either, since it appears we don't unlink the
>> sockets here

Despite your comment, I'd like to go with choice (3) for now. After lock_sock() became
free from delay caused by pagefault handling, we could consider updating to choice (1).


  parent reply	other threads:[~2021-07-10 13:34 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-27 13:11 [PATCH] " Tetsuo Handa
2021-07-07  9:43 ` [PATCH v2] " Tetsuo Handa
2021-07-07 18:20   ` Luiz Augusto von Dentz
2021-07-07 23:33     ` Tetsuo Handa
2021-07-08  1:00       ` LinMa
2021-07-09 13:50         ` Tetsuo Handa
2021-07-10 13:34       ` Tetsuo Handa [this message]
2021-07-13 11:27   ` [PATCH v3] " Tetsuo Handa
2021-07-14 19:20     ` Luiz Augusto von Dentz
2021-07-15  3:03       ` LinMa
2021-07-16  3:47         ` Desmond Cheong Zhi Xi
2021-07-16  4:11           ` Desmond Cheong Zhi Xi
2021-07-16 14:48             ` Tetsuo Handa
2021-07-16 15:26               ` LinMa
2021-07-17 15:41                 ` Yet Another Patch for CVE-2021-3573 LinMa
2021-07-17 15:45                   ` LinMa
2021-07-22  9:36                 ` [PATCH v3] Bluetooth: call lock_sock() outside of spinlock section Tetsuo Handa
2021-07-22  4:47               ` LinMa
2021-07-22  5:16                 ` Tetsuo Handa

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