syzbot found that the local_unlock_nested_bh() call was missing in some cases. WARNING: possible recursive locking detected syzkaller #0 Not tainted -------------------------------------------- syz.2.329/7421 is trying to acquire lock: ffffe8ffffd48888 ((&cell->bh_lock)){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline] ffffe8ffffd48888 ((&cell->bh_lock)){+...}-{3:3}, at: gro_cells_receive+0x404/0x790 net/core/gro_cells.c:30 but task is already holding lock: ffffe8ffffd48888 ((&cell->bh_lock)){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline] ffffe8ffffd48888 ((&cell->bh_lock)){+...}-{3:3}, at: gro_cells_receive+0x404/0x790 net/core/gro_cells.c:30 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock((&cell->bh_lock)); lock((&cell->bh_lock)); *** DEADLOCK *** Given the introduction of @have_bh_lock variable, it seems the author intent was to have the local_unlock_nested_bh() after the @unlock label. Fixes: 25718fdcbdd2 ("net: gro_cells: Use nested-BH locking for gro_cell") Reported-by: syzbot+f9651b9a8212e1c8906f@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/68f65eb9.a70a0220.205af.0034.GAE@google.com/T/#u Signed-off-by: Eric Dumazet Cc: Sebastian Andrzej Siewior --- net/core/gro_cells.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/net/core/gro_cells.c b/net/core/gro_cells.c index b43911562f4d10aa3d05c60f343ff89c5d9ed58d..fd57b845de333ff0e397eeb95aa67926d4e4a730 100644 --- a/net/core/gro_cells.c +++ b/net/core/gro_cells.c @@ -43,12 +43,11 @@ int gro_cells_receive(struct gro_cells *gcells, struct sk_buff *skb) if (skb_queue_len(&cell->napi_skbs) == 1) napi_schedule(&cell->napi); - if (have_bh_lock) - local_unlock_nested_bh(&gcells->cells->bh_lock); - res = NET_RX_SUCCESS; unlock: + if (have_bh_lock) + local_unlock_nested_bh(&gcells->cells->bh_lock); rcu_read_unlock(); return res; } -- 2.51.0.858.gf9c4a03a3a-goog