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Commit bc0a7438 authored by Ralf Baechle's avatar Ralf Baechle Committed by Jeff Garzik
Browse files

[PATCH] rcu in bpqether driver. 



From Suzanne Wood <suzannew@cs.pdx.edu>:

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: default avatarRalf Baechle DL5RB <ralf@linux-mips.org>
Signed-off-by: default avatarJeff Garzik <jgarzik@pobox.com>
parent ad4ebed0

drivers/net/hamradio/bpqether.c

+3 −6
Original line number Diff line number Diff line
@@ -144,7 +144,7 @@ static inline struct net_device *bpq_get_ax25_dev(struct net_device *dev) 
{

	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_file *seq, loff_t *pos) 
	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_file *seq, void *v, loff_t *pos) 
		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 notifier_block *this,unsigned long event, voi 
	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 notifier_block *this,unsigned long event, voi 
	default:

		break;

	}

	rcu_read_unlock();



	return NOTIFY_DONE;

}