• Jason A. Donenfeld's avatar
    ip_tunnel: disable preemption when updating per-cpu tstats · b4fe85f9
    Jason A. Donenfeld authored
    Drivers like vxlan use the recently introduced
    udp_tunnel_xmit_skb/udp_tunnel6_xmit_skb APIs. udp_tunnel6_xmit_skb
    makes use of ip6tunnel_xmit, and ip6tunnel_xmit, after sending the
    packet, updates the struct stats using the usual
    u64_stats_update_begin/end calls on this_cpu_ptr(dev->tstats).
    udp_tunnel_xmit_skb makes use of iptunnel_xmit, which doesn't touch
    tstats, so drivers like vxlan, immediately after, call
    iptunnel_xmit_stats, which does the same thing - calls
    u64_stats_update_begin/end on this_cpu_ptr(dev->tstats).
    
    While vxlan is probably fine (I don't know?), calling a similar function
    from, say, an unbound workqueue, on a fully preemptable kernel causes
    real issues:
    
    [  188.434537] BUG: using smp_processor_id() in preemptible [00000000] code: kworker/u8:0/6
    [  188.435579] caller is debug_smp_processor_id+0x17/0x20
    [  188.435583] CPU: 0 PID: 6 Comm: kworker/u8:0 Not tainted 4.2.6 #2
    [  188.435607] Call Trace:
    [  188.435611]  [<ffffffff8234e936>] dump_stack+0x4f/0x7b
    [  188.435615]  [<ffffffff81915f3d>] check_preemption_disabled+0x19d/0x1c0
    [  188.435619]  [<ffffffff81915f77>] debug_smp_processor_id+0x17/0x20
    
    The solution would be to protect the whole
    this_cpu_ptr(dev->tstats)/u64_stats_update_begin/end blocks with
    disabling preemption and then reenabling it.
    Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
    Acked-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    b4fe85f9
ip6_tunnel.h 3.23 KB