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mac80211: fix and simplify mesh locking

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The locking in mesh_{mpath,mpp}_table_grow not only
has an rcu_read_unlock() missing, it's also racy
(though really only technically since it's invoked
from a single function only) since it obtains the
new size of the table without any locking, so two
invocations of the function could attempt the same
resize.

Additionally, it uses synchronize_rcu() which is
rather expensive and can be avoided trivially here.

Modify the functions to only use the table lock
and use call_rcu() instead of synchronize_rcu().

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Johannes Berg 2011-05-14 11:00:52 +02:00 • committed by John W. Linville
parent d07c7cf49a
commit 1928ecab62
2 changed files with 25 additions and 22 deletions
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3
net/mac80211/mesh.h
View file

@ -120,6 +120,7 @@ struct mesh_path {
* buckets * buckets
* @mean_chain_len: maximum average length for the hash buckets' list, if it is * @mean_chain_len: maximum average length for the hash buckets' list, if it is
* reached, the table will grow * reached, the table will grow
* rcu_head: RCU head to free the table
*/ */
struct mesh_table { struct mesh_table {
/* Number of buckets will be 2^N */ /* Number of buckets will be 2^N */
@ -132,6 +133,8 @@ struct mesh_table {
int (*copy_node) (struct hlist_node *p, struct mesh_table *newtbl); int (*copy_node) (struct hlist_node *p, struct mesh_table *newtbl);
int size_order; int size_order;
int mean_chain_len; int mean_chain_len;
struct rcu_head rcu_head;
}; };
/* Recent multicast cache */ /* Recent multicast cache */

44
net/mac80211/mesh_pathtbl.c
View file

@ -370,52 +370,52 @@ err_path_alloc:
return err; return err;
} }
static void mesh_table_free_rcu(struct rcu_head *rcu)
{
struct mesh_table *tbl = container_of(rcu, struct mesh_table, rcu_head);
mesh_table_free(tbl, false);
}
void mesh_mpath_table_grow(void) void mesh_mpath_table_grow(void)
{ {
struct mesh_table *oldtbl, *newtbl; struct mesh_table *oldtbl, *newtbl;
rcu_read_lock();
newtbl = mesh_table_alloc(rcu_dereference(mesh_paths)->size_order + 1);
if (!newtbl)
return;
write_lock_bh(&pathtbl_resize_lock); write_lock_bh(&pathtbl_resize_lock);
newtbl = mesh_table_alloc(mesh_paths->size_order + 1);
if (!newtbl)
goto out;
oldtbl = mesh_paths; oldtbl = mesh_paths;
if (mesh_table_grow(mesh_paths, newtbl) < 0) { if (mesh_table_grow(mesh_paths, newtbl) < 0) {
rcu_read_unlock();
__mesh_table_free(newtbl); __mesh_table_free(newtbl);
write_unlock_bh(&pathtbl_resize_lock); goto out;
return;
} }
rcu_read_unlock();
rcu_assign_pointer(mesh_paths, newtbl); rcu_assign_pointer(mesh_paths, newtbl);
write_unlock_bh(&pathtbl_resize_lock);
synchronize_rcu(); call_rcu(&oldtbl->rcu_head, mesh_table_free_rcu);
mesh_table_free(oldtbl, false);
out:
write_unlock_bh(&pathtbl_resize_lock);
} }
void mesh_mpp_table_grow(void) void mesh_mpp_table_grow(void)
{ {
struct mesh_table *oldtbl, *newtbl; struct mesh_table *oldtbl, *newtbl;
rcu_read_lock();
newtbl = mesh_table_alloc(rcu_dereference(mpp_paths)->size_order + 1);
if (!newtbl)
return;
write_lock_bh(&pathtbl_resize_lock); write_lock_bh(&pathtbl_resize_lock);
newtbl = mesh_table_alloc(mpp_paths->size_order + 1);
if (!newtbl)
goto out;
oldtbl = mpp_paths; oldtbl = mpp_paths;
if (mesh_table_grow(mpp_paths, newtbl) < 0) { if (mesh_table_grow(mpp_paths, newtbl) < 0) {
rcu_read_unlock();
__mesh_table_free(newtbl); __mesh_table_free(newtbl);
write_unlock_bh(&pathtbl_resize_lock); goto out;
return;
} }
rcu_read_unlock();
rcu_assign_pointer(mpp_paths, newtbl); rcu_assign_pointer(mpp_paths, newtbl);
write_unlock_bh(&pathtbl_resize_lock); call_rcu(&oldtbl->rcu_head, mesh_table_free_rcu);
synchronize_rcu(); out:
mesh_table_free(oldtbl, false); write_unlock_bh(&pathtbl_resize_lock);
} }
int mpp_path_add(u8 *dst, u8 *mpp, struct ieee80211_sub_if_data *sdata) int mpp_path_add(u8 *dst, u8 *mpp, struct ieee80211_sub_if_data *sdata)