mac80211: Allocate new mesh path and portal tables before taking locks

It is unnecessary to hold the path table resize lock while allocating a
new table.  Allocate first and take lock later.  This resolves a
soft-lockup:

[  293.385799] BUG: soft lockup - CPU#0 stuck for 61s! [kworker/u:3:744]
(...)
[  293.386049] Call Trace:
[  293.386049]  [<c119fd04>] do_raw_read_lock+0x26/0x29
[  293.386049]  [<c14b2982>] _raw_read_lock+0x8/0xa
[  293.386049]  [<c148c178>] mesh_path_add+0xb7/0x24e
[  293.386049]  [<c148b98d>] ? mesh_path_lookup+0x1b/0xa6
[  293.386049]  [<c148ded5>] hwmp_route_info_get+0x276/0x2fd
[  293.386049]  [<c148dfb6>] mesh_rx_path_sel_frame+0x5a/0x5d9
[  293.386049]  [<c102667d>] ? update_curr+0x1cf/0x1d7
[  293.386049]  [<c148b45a>] ieee80211_mesh_rx_queued_mgmt+0x60/0x67
[  293.386049]  [<c147c374>] ieee80211_iface_work+0x1f0/0x258
(...)

Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 25 insertions, 24 deletions

diff --git a/net/mac80211/mesh_pathtbl.c b/net/mac80211/mesh_pathtbl.c
index 8d65b47d9837..7776ae5a8f15 100644
--- a/net/mac80211/mesh_pathtbl.c
+++ b/net/mac80211/mesh_pathtbl.c
@@ -65,42 +65,37 @@ void mesh_table_free(struct mesh_table *tbl, bool free_leafs)
         __mesh_table_free(tbl);
 }
 
-static struct mesh_table *mesh_table_grow(struct mesh_table *tbl)
+static int mesh_table_grow(struct mesh_table *oldtbl,
+                struct mesh_table *newtbl)
 {
-        struct mesh_table *newtbl;
         struct hlist_head *oldhash;
         struct hlist_node *p, *q;
         int i;
 
-        if (atomic_read(&tbl->entries)
-                        < tbl->mean_chain_len * (tbl->hash_mask + 1))
-                goto endgrow;
+        if (atomic_read(&oldtbl->entries)
+                        < oldtbl->mean_chain_len * (oldtbl->hash_mask + 1))
+                return -EAGAIN;
 
-        newtbl = mesh_table_alloc(tbl->size_order + 1);
-        if (!newtbl)
-                goto endgrow;
 
-        newtbl->free_node = tbl->free_node;
-        newtbl->mean_chain_len = tbl->mean_chain_len;
-        newtbl->copy_node = tbl->copy_node;
-        atomic_set(&newtbl->entries, atomic_read(&tbl->entries));
+        newtbl->free_node = oldtbl->free_node;
+        newtbl->mean_chain_len = oldtbl->mean_chain_len;
+        newtbl->copy_node = oldtbl->copy_node;
+        atomic_set(&newtbl->entries, atomic_read(&oldtbl->entries));
 
-        oldhash = tbl->hash_buckets;
-        for (i = 0; i <= tbl->hash_mask; i++)
+        oldhash = oldtbl->hash_buckets;
+        for (i = 0; i <= oldtbl->hash_mask; i++)
                 hlist_for_each(p, &oldhash[i])
-                        if (tbl->copy_node(p, newtbl) < 0)
+                        if (oldtbl->copy_node(p, newtbl) < 0)
                                 goto errcopy;
 
-        return newtbl;
+        return 0;
 
 errcopy:
         for (i = 0; i <= newtbl->hash_mask; i++) {
                 hlist_for_each_safe(p, q, &newtbl->hash_buckets[i])
-                        tbl->free_node(p, 0);
+                        oldtbl->free_node(p, 0);
         }
-        __mesh_table_free(newtbl);
-endgrow:
-        return NULL;
+        return -ENOMEM;
 }
 
 
@@ -334,10 +329,13 @@ void mesh_mpath_table_grow(void)
 {
         struct mesh_table *oldtbl, *newtbl;
 
+        newtbl = mesh_table_alloc(mesh_paths->size_order + 1);
+        if (!newtbl)
+                return;
         write_lock(&pathtbl_resize_lock);
         oldtbl = mesh_paths;
-        newtbl = mesh_table_grow(mesh_paths);
-        if (!newtbl) {
+        if (mesh_table_grow(mesh_paths, newtbl) < 0) {
+                __mesh_table_free(newtbl);
                 write_unlock(&pathtbl_resize_lock);
                 return;
         }
@@ -352,10 +350,13 @@ void mesh_mpp_table_grow(void)
 {
         struct mesh_table *oldtbl, *newtbl;
 
+        newtbl = mesh_table_alloc(mpp_paths->size_order + 1);
+        if (!newtbl)
+                return;
         write_lock(&pathtbl_resize_lock);
         oldtbl = mpp_paths;
-        newtbl = mesh_table_grow(mpp_paths);
-        if (!newtbl) {
+        if (mesh_table_grow(mpp_paths, newtbl) < 0) {
+                __mesh_table_free(newtbl);
                 write_unlock(&pathtbl_resize_lock);
                 return;
         }