On Wed, May 15, 2019 at 3:21 PM Thomas Pedersen <thomas@xxxxxxxx> wrote:
>
> ifmsh->csa was being dereferenced without the RCU read
> lock held.
>
> fixes the following warning:
>
> [ 74.930435] =============================
> [ 74.932066] WARNING: suspicious RCU usage
> [ 74.933671] 4.20.13 #5 Tainted: G W
> [ 74.935804] -----------------------------
> [ 74.937427] net/mac80211/mesh.c:1218 suspicious rcu_dereference_check() usage!
> [ 74.940473] other info that might help us debug this:
> [ 74.943654] rcu_scheduler_active = 2, debug_locks = 1
> [ 74.946311] 5 locks held by kworker/u8:3/107:
> [ 74.948087] #0: 000000007623c1f0 ((wq_completion)"%s"wiphy_name(local->hw.wiphy)){+.+.}, at: process_one_work+0x1a2/0x610
> [ 74.952464] #1: 00000000077b4215 ((work_completion)(&sdata->csa_finalize_work)){+.+.}, at: process_one_work+0x1a2/0x610
> [ 74.957228] #2: 00000000e02b12da (&wdev->mtx){+.+.}, at: ieee80211_csa_finalize_work+0x2f/0x90
> [ 74.959870] #3: 00000000e6855095 (&local->mtx){+.+.}, at: ieee80211_csa_finalize_work+0x47/0x90
> [ 74.962937] #4: 00000000bb5e3bca (&local->chanctx_mtx){+.+.}, at: ieee80211_csa_finalize_work+0x51/0x90
Sorry the commit message is a little out of date, I actually tested on
5.1.0-rc7-wt as well.
> Signed-off-by: Thomas Pedersen <thomas@xxxxxxxx>
> ---
> net/mac80211/mesh.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/mac80211/mesh.c b/net/mac80211/mesh.c
> index 766e5e5..70aeb34 100644
> --- a/net/mac80211/mesh.c
> +++ b/net/mac80211/mesh.c
> @@ -1220,10 +1220,12 @@ int ieee80211_mesh_finish_csa(struct ieee80211_sub_if_data *sdata)
> ifmsh->chsw_ttl = 0;
>
> /* Remove the CSA and MCSP elements from the beacon */
> + rcu_read_lock();
> tmp_csa_settings = rcu_dereference(ifmsh->csa);
> RCU_INIT_POINTER(ifmsh->csa, NULL);
> if (tmp_csa_settings)
> kfree_rcu(tmp_csa_settings, rcu_head);
> + rcu_read_unlock();
> ret = ieee80211_mesh_rebuild_beacon(sdata);
> if (ret)
> return -EINVAL;
> --
> 2.7.4
>
--
thomas
