• John Fastabend's avatar
    net: rcu lock and preempt disable missing around generic xdp · bbbe211c
    John Fastabend authored
    do_xdp_generic must be called inside rcu critical section with preempt
    disabled to ensure BPF programs are valid and per-cpu variables used
    for redirect operations are consistent. This patch ensures this is true
    and fixes the splat below.
    
    The netif_receive_skb_internal() code path is now broken into two rcu
    critical sections. I decided it was better to limit the preempt_enable/disable
    block to just the xdp static key portion and the fallout is more
    rcu_read_lock/unlock calls. Seems like the best option to me.
    
    [  607.596901] =============================
    [  607.596906] WARNING: suspicious RCU usage
    [  607.596912] 4.13.0-rc4+ #570 Not tainted
    [  607.596917] -----------------------------
    [  607.596923] net/core/dev.c:3948 suspicious rcu_dereference_check() usage!
    [  607.596927]
    [  607.596927] other info that might help us debug this:
    [  607.596927]
    [  607.596933]
    [  607.596933] rcu_scheduler_active = 2, debug_locks = 1
    [  607.596938] 2 locks held by pool/14624:
    [  607.596943]  #0:  (rcu_read_lock_bh){......}, at: [<ffffffff95445ffd>] ip_finish_output2+0x14d/0x890
    [  607.596973]  #1:  (rcu_read_lock_bh){......}, at: [<ffffffff953c8e3a>] __dev_queue_xmit+0x14a/0xfd0
    [  607.597000]
    [  607.597000] stack backtrace:
    [  607.597006] CPU: 5 PID: 14624 Comm: pool Not tainted 4.13.0-rc4+ #570
    [  607.597011] Hardware name: Dell Inc. Precision Tower 5810/0HHV7N, BIOS A17 03/01/2017
    [  607.597016] Call Trace:
    [  607.597027]  dump_stack+0x67/0x92
    [  607.597040]  lockdep_rcu_suspicious+0xdd/0x110
    [  607.597054]  do_xdp_generic+0x313/0xa50
    [  607.597068]  ? time_hardirqs_on+0x5b/0x150
    [  607.597076]  ? mark_held_locks+0x6b/0xc0
    [  607.597088]  ? netdev_pick_tx+0x150/0x150
    [  607.597117]  netif_rx_internal+0x205/0x3f0
    [  607.597127]  ? do_xdp_generic+0xa50/0xa50
    [  607.597144]  ? lock_downgrade+0x2b0/0x2b0
    [  607.597158]  ? __lock_is_held+0x93/0x100
    [  607.597187]  netif_rx+0x119/0x190
    [  607.597202]  loopback_xmit+0xfd/0x1b0
    [  607.597214]  dev_hard_start_xmit+0x127/0x4e0
    
    Fixes: d4455169 ("net: xdp: support xdp generic on virtual devices")
    Fixes: b5cdae32 ("net: Generic XDP")
    Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    Signed-off-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
    Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    bbbe211c
dev.c 217 KB