From: Jarek Poplawski > ======================================================= > [ INFO: possible circular locking dependency detected ] > 2.6.21-rc4 #1 > ------------------------------------------------------- > pppd/8926 is trying to acquire lock: > (&vlan_netdev_xmit_lock_key){-...}, at: [] > dev_queue_xmit+0x247/0x2f1 > > but task is already holding lock: > (&pch->downl){-+..}, at: [] ppp_channel_push+0x19/0x9a > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #3 (&pch->downl){-+..}: > [] __lock_acquire+0xe62/0x1010 > [] lock_acquire+0x69/0x83 > [] _spin_lock_bh+0x30/0x3d > [] ppp_push+0x5a/0x9a > [] ppp_xmit_process+0x2e/0x511 > [] ppp_write+0xb8/0xf2 > [] vfs_write+0x7f/0xba > [] sys_write+0x3d/0x64 > [] sysenter_past_esp+0x5f/0x99 > [] 0xffffffff > > -> #2 (&ppp->wlock){-+..}: > [] __lock_acquire+0xe62/0x1010 > [] lock_acquire+0x69/0x83 > [] _spin_lock_bh+0x30/0x3d > [] ppp_xmit_process+0x19/0x511 > [] ppp_start_xmit+0x18a/0x204 > [] dev_hard_start_xmit+0x1f6/0x2c4 > [] __qdisc_run+0x81/0x1bc > [] dev_queue_xmit+0x25f/0x2f1 > [] ip_output+0x1be/0x25f > [] ip_forward+0x159/0x22b > [] ip_rcv+0x297/0x4dd > [] netif_receive_skb+0x164/0x1f2 > [] e1000_clean_rx_irq+0x12a/0x4b7 > [] e1000_clean+0x3ff/0x5dd > [] net_rx_action+0x7d/0x12b > [] __do_softirq+0x82/0xf2 > [] do_softirq+0x57/0x59 > [] irq_exit+0x7f/0x81 > [] do_IRQ+0x45/0x84 > [] common_interrupt+0x2e/0x34 > [] mwait_idle+0x12/0x14 > [] cpu_idle+0x6c/0x86 > [] rest_init+0x23/0x36 > [] start_kernel+0x3ca/0x461 > [<00000000>] 0x0 > [] 0xffffffff > > -> #1 (&dev->_xmit_lock){-+..}: > [] __lock_acquire+0xe62/0x1010 > [] lock_acquire+0x69/0x83 > [] _spin_lock_bh+0x30/0x3d > [] dev_mc_add+0x34/0x16a > [] vlan_dev_set_multicast_list+0x88/0x25c > [] __dev_mc_upload+0x22/0x24 > [] dev_mc_add+0xe7/0x16a > [] igmp_group_added+0xe6/0xeb > [] ip_mc_inc_group+0x13f/0x210 > [] ip_mc_up+0x1e/0x61 > [] inetdev_event+0x154/0x2c7 > [] notifier_call_chain+0x2c/0x39 > [] raw_notifier_call_chain+0x8/0xa > [] dev_open+0x6d/0x71 > [] dev_change_flags+0x51/0x101 > [] devinet_ioctl+0x4df/0x644 > [] inet_ioctl+0x5c/0x6f > [] sock_ioctl+0x4f/0x1e8 > [] do_ioctl+0x22/0x71 > [] vfs_ioctl+0x55/0x27e > [] sys_ioctl+0x33/0x51 > [] sysenter_past_esp+0x5f/0x99 > [] 0xffffffff > > -> #0 (&vlan_netdev_xmit_lock_key){-...}: > [] __lock_acquire+0xcc0/0x1010 > [] lock_acquire+0x69/0x83 > [] _spin_lock+0x2b/0x38 > [] dev_queue_xmit+0x247/0x2f1 > [] __pppoe_xmit+0x1a9/0x215 > [] pppoe_xmit+0xa/0xc > [] ppp_channel_push+0x41/0x9a > [] ppp_write+0xc6/0xf2 > [] vfs_write+0x7f/0xba > [] sys_write+0x3d/0x64 > [] sysenter_past_esp+0x5f/0x99 > [] 0xffffffff > > other info that might help us debug this: > > 1 lock held by pppd/8926: > #0: (&pch->downl){-+..}, at: [] ppp_channel_push+0x19/0x9a > > stack backtrace: > [] show_trace_log_lvl+0x1a/0x30 > [] show_trace+0x12/0x14 > [] dump_stack+0x16/0x18 > [] print_circular_bug_tail+0x68/0x71 > [] __lock_acquire+0xcc0/0x1010 > [] lock_acquire+0x69/0x83 > [] _spin_lock+0x2b/0x38 > [] dev_queue_xmit+0x247/0x2f1 > [] __pppoe_xmit+0x1a9/0x215 > [] pppoe_xmit+0xa/0xc > [] ppp_channel_push+0x41/0x9a > [] ppp_write+0xc6/0xf2 > [] vfs_write+0x7f/0xba > [] sys_write+0x3d/0x64 > [] sysenter_past_esp+0x5f/0x99 > ======================= > Clocksource tsc unstable (delta = 4686844667 ns) > Time: acpi_pm clocksource has been installed. ... lockdep has seen locks "-> #0" - "-> #3" taken in circular order, but IMHO, lock "-> #3" (&pch->downl) taken after "-> #2" (&ppp->wlock) differs from &pch->downl lock taken in "-> #0" (before &vlan_netdev_xmit_lock_key) and lockdep should be notified about this. Reported & tested by: "Yuriy N. Shkandybin" Signed-off-by: Jarek Poplawski Cc: Paul Mackerras Signed-off-by: Andrew Morton --- drivers/net/ppp_generic.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff -puN drivers/net/ppp_generic.c~ppp_generic-fix-lockdep-warning drivers/net/ppp_generic.c --- a/drivers/net/ppp_generic.c~ppp_generic-fix-lockdep-warning +++ a/drivers/net/ppp_generic.c @@ -1433,7 +1433,8 @@ ppp_channel_push(struct channel *pch) struct sk_buff *skb; struct ppp *ppp; - spin_lock_bh(&pch->downl); + local_bh_disable(); + spin_lock_nested(&pch->downl, SINGLE_DEPTH_NESTING); if (pch->chan != 0) { while (!skb_queue_empty(&pch->file.xq)) { skb = skb_dequeue(&pch->file.xq); @@ -1447,7 +1448,8 @@ ppp_channel_push(struct channel *pch) /* channel got deregistered */ skb_queue_purge(&pch->file.xq); } - spin_unlock_bh(&pch->downl); + spin_unlock(&pch->downl); + local_bh_enable(); /* see if there is anything from the attached unit to be sent */ if (skb_queue_empty(&pch->file.xq)) { read_lock_bh(&pch->upl); _