On (02/09/17 19:19), Eric Dumazet wrote: > > More likely the bug is in fanout_add(), with a buggy sequence in error > case, and not correct locking. > > kfree(po->rollover); > po->rollover = NULL; > > Two cpus entering fanout_add() (using the same af_packet socket, > syzkaller courtesy...) might both see po->fanout being NULL. > > Then they grab the mutex. Too late...
I'm not sure I follow- aiui the panic was in acceessing the sk_receive_queue.lock in a socket that had been closed earlier. I think the assumption is that rcu_read_lock_bh in __dev_queue_xmit (and rcu_read_lock in dev_queue_xmit_nit?) should make sure that the nit packet delivery can be done safely, and the synchronize_net in packet_release() makes sure that the Tx paths are quiesced before freeing the socket. What is the race-hole here? Does it have to do with the _bh and softirq context, somehow? --Sowmini
