[Please remeber to CC netfilter-devel]
Pavel Emelyanov wrote:
Consider we are putting a clusterip_config entry with the "entries"
count == 1, and on the other CPU there's a clusterip_config_find_get
in progress:
CPU1: CPU2:
clusterip_config_entry_put: clusterip_config_find_get:
if (atomic_dec_and_test(&c->entries)) {
/* true */
read_lock_bh(&clusterip_lock);
c = __clusterip_config_find(clusterip);
/* found - it's still in list */
...
atomic_inc(&c->entries);
read_unlock_bh(&clusterip_lock);
write_lock_bh(&clusterip_lock);
list_del(&c->list);
write_unlock_bh(&clusterip_lock);
...
dev_put(c->dev);
Oops! We have an entry returned by the clusterip_config_find_get,
which is a) not in list b) has a stale dev pointer.
The problems will happen when the CPU2 will release the entry - it
will remove it from the list for the 2nd time, thus spoiling it, and
will put a stale dev pointer.
The fix is to make atomic_dec_and_test under the clusterip_lock.
I guess an alternative would have been to use atomic_inc_not_zero
in clusterip_config_find_get. But this is only called very rarely,
so it doesn't really matter.
Applied, thanks.
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