[PATCH 03/10] mac80211: mesh: fix RCU warning

Lee Jones
2019-11-07T20:17:46Z

From: Thomas Pedersen <thomas@eero.com>

[ Upstream commit 551842446ed695641a00782cd118cbb064a416a1 ]

ifmsh->csa is an RCU-protected pointer. The writer context
in ieee80211_mesh_finish_csa() is already mutually
exclusive with wdev->sdata.mtx, but the RCU checker did
not know this. Use rcu_dereference_protected() to avoid a
warning.

fixes the following warning:

[ 12.519089] =============================
[ 12.520042] WARNING: suspicious RCU usage
[ 12.520652] 5.1.0-rc7-wt+ #16 Tainted: G W
[ 12.521409] -----------------------------
[ 12.521972] net/mac80211/mesh.c:1223 suspicious rcu_dereference_check() usage!
[ 12.522928] other info that might help us debug this:
[ 12.523984] rcu_scheduler_active = 2, debug_locks = 1
[ 12.524855] 5 locks held by kworker/u8:2/152:
[ 12.525438] #0: 00000000057be08c ((wq_completion)phy0){+.+.}, at: process_one_work+0x1a2/0x620
[ 12.526607] #1: 0000000059c6b07a ((work_completion)(&sdata->csa_finalize_work)){+.+.}, at: process_one_work+0x1a2/0x620
[ 12.528001] #2: 00000000f184ba7d (&wdev->mtx){+.+.}, at: ieee80211_csa_finalize_work+0x2f/0x90
[ 12.529116] #3: 00000000831a1f54 (&local->mtx){+.+.}, at: ieee80211_csa_finalize_work+0x47/0x90
[ 12.530233] #4: 00000000fd06f988 (&local->chanctx_mtx){+.+.}, at: ieee80211_csa_finalize_work+0x51/0x90

Signed-off-by: Thomas Pedersen <thomas@eero.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Change-Id: I19313f756382b0078683036d50c6645dd8ab2bee
---
net/mac80211/mesh.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/mac80211/mesh.c b/net/mac80211/mesh.c
index a70c970a743a..06189c952291 100644
--- a/net/mac80211/mesh.c
+++ b/net/mac80211/mesh.c
@@ -1062,7 +1062,8 @@ int ieee80211_mesh_finish_csa(struct ieee80211_sub_if_data *sdata)
ifmsh->chsw_ttl = 0;

/* Remove the CSA and MCSP elements from the beacon */
- tmp_csa_settings = rcu_dereference(ifmsh->csa);
+ tmp_csa_settings = rcu_dereference_protected(ifmsh->csa,
+ lockdep_is_held(&sdata->wdev.mtx));
RCU_INIT_POINTER(ifmsh->csa, NULL);
if (tmp_csa_settings)
kfree_rcu(tmp_csa_settings, rcu_head);
@@ -1084,6 +1085,8 @@ int ieee80211_mesh_csa_beacon(struct ieee80211_sub_if_data *sdata,
struct mesh_csa_settings *tmp_csa_settings;
int ret = 0;

+ lockdep_assert_held(&sdata->wdev.mtx);
+
tmp_csa_settings = kmalloc(sizeof(*tmp_csa_settings),
GFP_ATOMIC);
if (!tmp_csa_settings)