On Sat, 2012-01-21 at 22:19 +0200, alex wrote: [...] > [148654.740747] xt_TCPMSS: bad length (41 bytes) > [148656.341170] BUG: scheduling while atomic: ksoftirqd/0/4/0x10000100 > [148656.341402] Modules linked in: act_police sch_ingress cls_u32 sch_sfq > sch_cbq dummy 8021q garp stp xt_TCPMSS ipt_REJECT xt_tcpudp xt_state > xt_multiport iptable_filt > er iptable_nat nf_nat nf_conntrack_ipv4 nf_conntrack nf_defrag_ipv4 ip_tables > x_tables xfs exportfs pppoe pppol2tp pptp pppox ppp_generic slhc loop > firewire_sbp2 snd_hd > a_codec_realtek snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_timer > nouveau ttm drm_kms_helper snd drm i2c_piix4 i2c_algo_bit i2c_core k10temp > soundcore edac_core s > nd_page_alloc edac_mce_amd pcspkr button wmi evdev processor ext3 jbd mbcache > ata_generic sd_mod crc_t10dif ohci_hcd pata_via pata_atiixp tg3 libphy ahci > ehci_hcd libat > a ixgbe xhci firewire_ohci dca floppy usbcore thermal scsi_mod firewire_core > nls_base crc_itu_t thermal_sys [last unloaded: scsi_wait_scan] > [148656.341440] Pid: 4, comm: ksoftirqd/0 Not tainted 2.6.32-5-amd64 #1 > [148656.341442] Call Trace: > [148656.341443] <IRQ> [<ffffffff812facb8>] ? schedule+0xc5/0x7b4 > [148656.341453] [<ffffffff810963c9>] ? handle_edge_irq+0xdd/0x101 > [148656.341457] [<ffffffff8104aa4c>] ? __cond_resched+0x1d/0x26 > [148656.341459] [<ffffffff812fb5ab>] ? _cond_resched+0x24/0x2f > [148656.341463] [<ffffffff81243945>] ? lock_sock_nested+0x16/0xab > [148656.341465] [<ffffffff810114d3>] ? ret_from_intr+0x0/0x11 > [148656.341469] [<ffffffffa01a6b2a>] ? pppol2tp_tunnel_destruct+0xe7/0x1f7 > [pppol2tp] > [148656.341472] [<ffffffff8124433f>] ? __sk_free+0x15/0xe8 > [148656.341474] [<ffffffff81247c06>] ? skb_release_head_state+0x6d/0xc8 > [148656.341476] [<ffffffff8124797a>] ? __kfree_skb+0x9/0x7d > [148656.341485] [<ffffffffa00cf989>] ? ixgbe_poll+0x119/0x1840 [ixgbe] > [148656.341489] [<ffffffff81272e08>] ? ip_rcv_finish+0x0/0x38d > [148656.341493] [<ffffffff8124fd8e>] ? net_rx_action+0xae/0x1c9 > [148656.341496] [<ffffffff81053d2b>] ? __do_softirq+0xdd/0x1a6 > [148656.341498] [<ffffffff81011cac>] ? call_softirq+0x1c/0x30 [...]
It appears that a transmit completion results in dropping the last reference to a PPPoL2TP tunnel, causing it to be destroyed. pppo2ltp_tunnel_destruct() calls pppo2ltp_tunnel_closeall() (inlined here) which calls lock_sock(), and that may sleep. Although this was observed in 2.6.32, the bug appears to be present today: l2tp_tunnel_destruct() calls l2tp_tunnel_closeall() calls pppol2tp_session_close() calls lock_sock(). But maybe this is actually a ref-counting bug and the tunnel should never actually be destroyed in atomic context. Ben. -- Ben Hutchings Knowledge is power. France is bacon.
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