On Mon, Aug 29, 2011 at 6:49 AM, Johannes Berg
<johannes@xxxxxxxxxxxxxxxx> wrote:
> On Fri, 2011-08-26 at 17:18 -0700, Javier Cardona wrote:
>> Signed-off-by: Javier Cardona <javier@xxxxxxxxxxx>
>>
>> ---
>> v2: - Fix extra space (checkpatch)
>> - Add lockdep check for RCU
>> net/mac80211/mesh_pathtbl.c | 65 +++++++++++++++++-------------------------
>> 1 files changed, 26 insertions(+), 39 deletions(-)
>>
>> diff --git a/net/mac80211/mesh_pathtbl.c b/net/mac80211/mesh_pathtbl.c
>> index ea9e34a..3c03be9 100644
>> --- a/net/mac80211/mesh_pathtbl.c
>> +++ b/net/mac80211/mesh_pathtbl.c
>> @@ -790,35 +790,6 @@ void mesh_plink_broken(struct sta_info *sta)
>> rcu_read_unlock();
>> }
>>
>> -/**
>> - * mesh_path_flush_by_nexthop - Deletes mesh paths if their next hop matches
>> - *
>> - * @sta - mesh peer to match
>> - *
>> - * RCU notes: this function is called when a mesh plink transitions from
>> - * PLINK_ESTAB to any other state, since PLINK_ESTAB state is the only one that
>> - * allows path creation. This will happen before the sta can be freed (because
>> - * sta_info_destroy() calls this) so any reader in a rcu read block will be
>> - * protected against the plink disappearing.
>> - */
>> -void mesh_path_flush_by_nexthop(struct sta_info *sta)
>> -{
>> - struct mesh_table *tbl;
>> - struct mesh_path *mpath;
>> - struct mpath_node *node;
>> - struct hlist_node *p;
>> - int i;
>> -
>> - rcu_read_lock();
>> - tbl = rcu_dereference(mesh_paths);
>> - for_each_mesh_entry(tbl, p, node, i) {
>> - mpath = node->mpath;
>> - if (rcu_dereference(mpath->next_hop) == sta)
>> - mesh_path_del(mpath->dst, mpath->sdata);
>> - }
>> - rcu_read_unlock();
>> -}
>> -
>> static void mesh_path_node_reclaim(struct rcu_head *rp)
>> {
>> struct mpath_node *node = container_of(rp, struct mpath_node, rcu);
>> @@ -845,7 +816,18 @@ static void __mesh_path_del(struct mesh_table *tbl, struct mpath_node *node)
>> atomic_dec(&tbl->entries);
>> }
>>
>> -static void mesh_path_flush(struct ieee80211_sub_if_data *sdata)
>> +/**
>> + * mesh_path_flush_by_nexthop - Deletes mesh paths if their next hop matches
>> + *
>> + * @sta - mesh peer to match
>> + *
>> + * RCU notes: this function is called when a mesh plink transitions from
>> + * PLINK_ESTAB to any other state, since PLINK_ESTAB state is the only one that
>> + * allows path creation. This will happen before the sta can be freed (because
>> + * sta_info_destroy() calls this) so any reader in a rcu read block will be
>> + * protected against the plink disappearing.
>> + */
>> +void mesh_path_flush_by_nexthop(struct sta_info *sta)
>> {
>> struct mesh_table *tbl;
>> struct mesh_path *mpath;
>> @@ -857,7 +839,7 @@ static void mesh_path_flush(struct ieee80211_sub_if_data *sdata)
>> tbl = rcu_dereference(mesh_paths);
>> for_each_mesh_entry(tbl, p, node, i) {
>> mpath = node->mpath;
>> - if (mpath->sdata == sdata) {
>> + if (rcu_dereference(mpath->next_hop) == sta) {
>> spin_lock_bh(&tbl->hashwlock[i]);
>> __mesh_path_del(tbl, node);
>> spin_unlock_bh(&tbl->hashwlock[i]);
>> @@ -866,24 +848,23 @@ static void mesh_path_flush(struct ieee80211_sub_if_data *sdata)
>> rcu_read_unlock();
>> }
>>
>> -static void mpp_path_flush(struct ieee80211_sub_if_data *sdata)
>> +static void table_flush_by_iface(struct mesh_table *tbl,
>> + struct ieee80211_sub_if_data *sdata)
>> {
>> - struct mesh_table *tbl;
>> struct mesh_path *mpath;
>> struct mpath_node *node;
>> struct hlist_node *p;
>> int i;
>>
>> - read_lock_bh(&pathtbl_resize_lock);
>> - tbl = rcu_dereference_protected(mpp_paths,
>> - lockdep_is_held(pathtbl_resize_lock));
>> + WARN_ON(!rcu_read_lock_held());
>> for_each_mesh_entry(tbl, p, node, i) {
>> mpath = node->mpath;
>> + if (mpath->sdata != sdata)
>> + continue;
>> spin_lock_bh(&tbl->hashwlock[i]);
>> __mesh_path_del(tbl, node);
>> spin_unlock_bh(&tbl->hashwlock[i]);
>> }
>> - read_unlock_bh(&pathtbl_resize_lock);
>> }
>
> So what protects against the table being grown at the same time? A copy
> will be made, but here you'll be iterating the old table -- which won't
> crash or anything but is semantically incorrect.
You are right. And I believe it actually may crash, given that the
nodes we wanted to delete will still exist in the new table. I'll
re-spin right away.
Thanks!
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