bpqether: fix rcu usage

The rcu_dereference() primitive needs to be applied to an l-value in order to
ensure that compiler writers don't get an opportunity to apply reordering
optimizations that could result in multiple fetches or in other misbehavior.
This patch pulls the rcu_dereference() calls in bpq_seq_next() up to the point
at which the fetched pointers are still l-values, rather than after
list_entry() has transformed them into r-values.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/net/hamradio/bpqether.c b/drivers/net/hamradio/bpqether.c
index 656f278..cc0ee93 100644 (file)
--- a/drivers/net/hamradio/bpqether.c
+++ b/drivers/net/hamradio/bpqether.c
@@ -413,12 +413,12 @@ static void *bpq_seq_next(struct seq_file *seq, void *v, loff_t *pos)
        ++*pos;
 
        if (v == SEQ_START_TOKEN)
-               p = bpq_devices.next;
+               p = rcu_dereference(bpq_devices.next);
        else
-               p = ((struct bpqdev *)v)->bpq_list.next;
+               p = rcu_dereference(((struct bpqdev *)v)->bpq_list.next);
 
        return (p == &bpq_devices) ? NULL 
-               : rcu_dereference(list_entry(p, struct bpqdev, bpq_list));
+               : list_entry(p, struct bpqdev, bpq_list);
 }
 
 static void bpq_seq_stop(struct seq_file *seq, void *v)