[PATCH] bluetooth: fix locking in hci_sock_dev_event()

[PATCH] bluetooth: fix locking in hci_sock_dev_event()

[Satyam Sharma]

[PATCH] bluetooth: fix locking in hci_sock_dev_event()

We presently use lock_sock() to acquire a lock on a socket in
hci_sock_dev_event(), but this goes BUG because lock_sock()
can sleep and we're already holding a read-write spinlock at
that point. So, we must use the non-sleeping BH version,
bh_lock_sock().

However, hci_sock_dev_event() is called from user context and
hence using simply bh_lock_sock() will deadlock against a
concurrent softirq that tries to acquire a lock on the same
socket. Hence, disabling BH's before acquiring the socket lock
and enable them afterwards, is the proper solution to fix
socket locking in hci_sock_dev_event().

Cc: David Miller <davem@davemloft.net>
Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

---

  net/bluetooth/hci_sock.c |    6 ++++--
  1 file changed, 4 insertions(+), 2 deletions(-)

---

diff -ruNp a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
--- a/net/bluetooth/hci_sock.c	2007-05-16 17:31:06.000000000 +0530
+++ b/net/bluetooth/hci_sock.c	2007-05-16 17:38:35.000000000 +0530
@@ -665,7 +665,8 @@ static int hci_sock_dev_event(struct not
  		/* Detach sockets from device */
  		read_lock(&hci_sk_list.lock);
  		sk_for_each(sk, node, &hci_sk_list.head) {
-			lock_sock(sk);
+			local_bh_disable();
+			bh_lock_sock_nested(sk);
  			if (hci_pi(sk)->hdev == hdev) {
  				hci_pi(sk)->hdev = NULL;
  				sk->sk_err = EPIPE;
@@ -674,7 +675,8 @@ static int hci_sock_dev_event(struct not

  				hci_dev_put(hdev);
  			}
-			release_sock(sk);
+			bh_unlock_sock(sk);
+			local_bh_enable();
  		}
  		read_unlock(&hci_sk_list.lock);
  	}

Re: [PATCH] bluetooth: fix locking in hci_sock_dev_event()

[David Miller]

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
Date: Thu, 17 May 2007 11:13:36 +0530 (IST)

> [PATCH] bluetooth: fix locking in hci_sock_dev_event()
> 
> We presently use lock_sock() to acquire a lock on a socket in
> hci_sock_dev_event(), but this goes BUG because lock_sock()
> can sleep and we're already holding a read-write spinlock at
> that point. So, we must use the non-sleeping BH version,
> bh_lock_sock().
> 
> However, hci_sock_dev_event() is called from user context and
> hence using simply bh_lock_sock() will deadlock against a
> concurrent softirq that tries to acquire a lock on the same
> socket. Hence, disabling BH's before acquiring the socket lock
> and enable them afterwards, is the proper solution to fix
> socket locking in hci_sock_dev_event().
> 
> Cc: David Miller <davem@davemloft.net>
> Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>
> Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Thanks I'll merge this in.

Re: [PATCH] bluetooth: fix locking in hci_sock_dev_event()

[David Miller]

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
Date: Thu, 17 May 2007 11:13:36 +0530 (IST)

> [PATCH] bluetooth: fix locking in hci_sock_dev_event()

BTW, your email client corrupted the patch spaces and tabs
a lot, I applied your patch by hand but I will not do that
next time.  Please look into getting your email client to
not corrupt the patches you send out, thank you.

Re: [PATCH] bluetooth: fix locking in hci_sock_dev_event()

[Satyam Sharma]

On Wed, 16 May 2007, David Miller wrote:
> From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
> Date: Thu, 17 May 2007 11:13:36 +0530 (IST)
>
>> [PATCH] bluetooth: fix locking in hci_sock_dev_event()
>
> BTW, your email client corrupted the patch spaces and tabs
> a lot, I applied your patch by hand but I will not do that
> next time.  Please look into getting your email client to
> not corrupt the patches you send out, thank you.

Ick. That's the second time pine did that to me. Doesn't seem
to happen consistently/reproducibly, but I'll try to fix it
nonetheless, thanks.

Satyam