From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ralf Baechle Subject: [PATCH] rcu in bpqether driver. Date: Mon, 17 Oct 2005 12:42:32 +0100 Message-ID: <20051017114232.GA7888@linux-mips.org> Mime-Version: 1.0 Return-path: Content-Disposition: inline Sender: linux-hams-owner@vger.kernel.org List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Jeff Garzik Cc: Suzanne Wood , linux-hams@vger.kernel.org >From Suzanne Wood : Clarify RCU implementation in bpqether.c. Because bpq_new_device() calls list_add_rcu() and bpq_free_device() calls list_del_rcu(), substitute list_for_each_entry_rcu() for list_for_each_entry() in bpq_get_ax25_dev() and in bpq_seq_start(). Add rcu dereference protection in bpq_seq_next(). The rcu_read_lock()/unlock() in bpq_device_event() are removed because netdev event handlers are called with RTNL locking in place. FYI: bpq_free_device() calls list_del_rcu() which, per list.h, requires synchronize_rcu() which can block or call_rcu() or call_rcu_bh() which cannot block. Herbert Xu notes that synchronization is done here by unregister_netdevice(). This calls synchronize_net() which in turn uses synchronize_rcu(). Signed-off-by: Ralf Baechle DL5RB drivers/net/hamradio/bpqether.c | 9 +++------ 1 files changed, 3 insertions(+), 6 deletions(-) Index: net-git/drivers/net/hamradio/bpqether.c =================================================================== --- net-git.orig/drivers/net/hamradio/bpqether.c +++ net-git/drivers/net/hamradio/bpqether.c @@ -144,7 +144,7 @@ static inline struct net_device *bpq_get { struct bpqdev *bpq; - list_for_each_entry(bpq, &bpq_devices, bpq_list) { + list_for_each_entry_rcu(bpq, &bpq_devices, bpq_list) { if (bpq->ethdev == dev) return bpq->axdev; } @@ -399,7 +399,7 @@ static void *bpq_seq_start(struct seq_fi if (*pos == 0) return SEQ_START_TOKEN; - list_for_each_entry(bpqdev, &bpq_devices, bpq_list) { + list_for_each_entry_rcu(bpqdev, &bpq_devices, bpq_list) { if (i == *pos) return bpqdev; } @@ -418,7 +418,7 @@ static void *bpq_seq_next(struct seq_fil p = ((struct bpqdev *)v)->bpq_list.next; return (p == &bpq_devices) ? NULL - : list_entry(p, struct bpqdev, bpq_list); + : rcu_dereference(list_entry(p, struct bpqdev, bpq_list)); } static void bpq_seq_stop(struct seq_file *seq, void *v) @@ -561,8 +561,6 @@ static int bpq_device_event(struct notif if (!dev_is_ethdev(dev)) return NOTIFY_DONE; - rcu_read_lock(); - switch (event) { case NETDEV_UP: /* new ethernet device -> new BPQ interface */ if (bpq_get_ax25_dev(dev) == NULL) @@ -581,7 +579,6 @@ static int bpq_device_event(struct notif default: break; } - rcu_read_unlock(); return NOTIFY_DONE; }