Re: 2.6.17-mm3 -- BUG: illegal lock usage -- illegal {softirq-on-W} -> {in-softirq-R} usage.

[Andrew Morton <akpm@osdl.org>]

On Thu, 29 Jun 2006 12:01:06 -0700
"Miles Lane" <miles.lane@gmail.com> wrote:

> [ BUG: illegal lock usage! ]
> ----------------------------

This is claiming that we're taking sk->sk_dst_lock in a deadlockable manner.

> illegal {softirq-on-W} -> {in-softirq-R} usage.

It found someone doing write_lock(sk_dst_lock) with softirqs enabled, but
someone else takes read_lock(dst_lock) inside softirqs.

> java_vm/4418 [HC0[0]:SC1[1]:HE1:SE0] takes:
>  (&sk->sk_dst_lock){---?}, at: [<c119d0a9>] sk_dst_check+0x1b/0xe6
> {softirq-on-W} state was registered at:
>   [<c102d1c8>] lock_acquire+0x60/0x80
>   [<c12012d7>] _write_lock+0x23/0x32
>   [<c11ddbe7>] inet_bind+0x16c/0x1cc
>   [<c119ae58>] sys_bind+0x61/0x80
>   [<c119b465>] sys_socketcall+0x7d/0x186
>   [<c1002d6d>] sysenter_past_esp+0x56/0x8d

	inet_bind()
	->sk_dst_get
	  ->read_lock(&sk->sk_dst_lock)

> irq event stamp: 11052
> hardirqs last  enabled at (11052): [<c105d454>] kmem_cache_alloc+0x89/0xa6
> hardirqs last disabled at (11051): [<c105d405>] kmem_cache_alloc+0x3a/0xa6
> softirqs last  enabled at (11040): [<c11a506d>] dev_queue_xmit+0x224/0x24b
> softirqs last disabled at (11041): [<c1004a64>] do_softirq+0x58/0xbd
> 
> other info that might help us debug this:
> 1 lock held by java_vm/4418:
>  #0:  (af_family_keys + (sk)->sk_family#4){-+..}, at: [<f93c9281>]
> tcp_v6_rcv+0x308/0x7b7 [ipv6]

	softirq
	->ip6_dst_lookup
	  ->sk_dst_check
	    ->sk_dst_reset
	      ->write_lock(&sk->sk_dst_lock);

> stack backtrace:
>  [<c1003502>] show_trace_log_lvl+0x54/0xfd
>  [<c1003b6a>] show_trace+0xd/0x10
>  [<c1003c0e>] dump_stack+0x19/0x1b
>  [<c102b833>] print_usage_bug+0x1cc/0x1d9
>  [<c102bd34>] mark_lock+0x193/0x360
>  [<c102c94a>] __lock_acquire+0x3b7/0x970
>  [<c102d1c8>] lock_acquire+0x60/0x80
>  [<c12013eb>] _read_lock+0x23/0x32
>  [<c119d0a9>] sk_dst_check+0x1b/0xe6
>  [<f93ae479>] ip6_dst_lookup+0x31/0x172 [ipv6]
>  [<f93c7065>] tcp_v6_send_synack+0x10f/0x238 [ipv6]
>  [<f93c7dc5>] tcp_v6_conn_request+0x281/0x2c7 [ipv6]
>  [<c11cca33>] tcp_rcv_state_process+0x5d/0xbde
>  [<f93c7414>] tcp_v6_do_rcv+0x26d/0x384 [ipv6]
>  [<f93c96d6>] tcp_v6_rcv+0x75d/0x7b7 [ipv6]
>  [<f93afadd>] ip6_input+0x201/0x2d1 [ipv6]
>  [<f93b002d>] ipv6_rcv+0x190/0x1bf [ipv6]
>  [<c11a3200>] netif_receive_skb+0x2e6/0x37f
>  [<c11a4b81>] process_backlog+0x80/0x112
>  [<c11a4c9e>] net_rx_action+0x8b/0x1e8
>  [<c101a711>] __do_softirq+0x55/0xb0
>  [<c1004a64>] do_softirq+0x58/0xbd
>  [<c101a978>] local_bh_enable+0xd0/0x107
>  [<c11a506d>] dev_queue_xmit+0x224/0x24b
>  [<c11a9bb8>] neigh_resolve_output+0x1e2/0x20e
>  [<f93add64>] ip6_output2+0x1de/0x1fc [ipv6]
>  [<f93ae41e>] ip6_output+0x69c/0x6c6 [ipv6]
>  [<f93aeb58>] ip6_xmit+0x22b/0x295 [ipv6]
>  [<f93cc893>] inet6_csk_xmit+0x200/0x20e [ipv6]
>  [<c11cea04>] tcp_transmit_skb+0x5de/0x60c
>  [<c11d0cd7>] tcp_connect+0x2bb/0x31a
>  [<f93c894a>] tcp_v6_connect+0x520/0x655 [ipv6]
>  [<c11dd889>] inet_stream_connect+0x83/0x20f
>  [<c119adda>] sys_connect+0x67/0x84
>  [<c119b474>] sys_socketcall+0x8c/0x186
>  [<c1002d6d>] sysenter_past_esp+0x56/0x8d

So the allegation is that if a softirq runs sk_dst_reset() while
process-context code is running sk_dst_set(), we'll do write_lock() while
holding read_lock().  
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