linux-kernel - [PATCH] bluetooth: fix locking in hci_sock_dev

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Date:	Thu, 17 May 2007 11:13:36 +0530 (IST)
From:	Satyam Sharma <ssatyam@....iitk.ac.in>
To:	akpm@...ux-foundation.org
cc:	David Miller <davem@...emloft.net>,
	Marcel Holtmann <marcel@...tmann.org>,
	Jiri Kosina <jikos@...os.cz>, Greg KH <gregkh@...e.de>,
	Jeremy Fitzhardinge <jeremy@...p.org>, maxk@...lcomm.com,
	Cedric Le Goater <clg@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] bluetooth: fix locking in hci_sock_dev_event()

[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@...emloft.net>
Signed-off-by: Satyam Sharma <ssatyam@....iitk.ac.in>
Signed-off-by: Marcel Holtmann <marcel@...tmann.org>
Signed-off-by: Jiri Kosina <jkosina@...e.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);
  	}

-
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