Many thanks for your direction and insights.
> From [email protected] Sat Oct 15 01:05:52 2005
> On Sat, Oct 15, 2005 at 12:57:23AM -0700, Suzanne Wood wrote:
> >
> > Another list_for_each_entry() in bpq_seq_start() in a marked rcu
> > read-side critical section becomes the rcu version.
> You might want to add an rcu_dereference in bpq_seq_next
> as well.
Please find attached a patch to drivers/net/hamradio/bpqether.c
that might finally merit being
Signed-off-by: [email protected]
-------
ChangeLog: clarify RCU implementation in
drivers/net/hamradio/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().
-------
bpqether.c | 9 +++------
1 files changed, 3 insertions(+), 6 deletions(-)
-------
--- src/linux-2.6.14-rc4/drivers/net/hamradio/bpqether.c 2005-10-10 18:19:19.000000000 -0700
+++ patch/linux-2.6.14-rc4/drivers/net/hamradio/bpqether.c 2005-10-15 15:12:15.000000000 -0700
@@ -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;
}
-
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