On Fri, 4 Apr 2008 10:43:02 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

quoted text
> On Fri, 04 Apr 2008 17:45:36 +0200 Johannes Berg <johannes@sipsolutions.net> wrote:
> 
> > 
> > On Thu, 2008-04-03 at 10:41 -0400, Miles Lane wrote:
> > > After collecting the wireshark log, I found this in my messages log:
> > 
> > Below is a better version of the trace Miles sent me privately, but I
> > have no idea what would be causing it. I don't think it's related to
> > wireless.
> > 
> > ___=======================================================
> > [ INFO: possible circular locking dependency detected ]
> > 2.6.25-rc8-mm1 #15
> > -------------------------------------------------------
> > iw/9417 is trying to acquire lock:
> > (genl_mutex){--..}, at: [ctrl_dumpfamily+0x37/0xda] ctrl_dumpfamily+0x37/0xda
> > 
> > but task is already holding lock:
> > (nlk->cb_mutex){--..}, at: [netlink_dump+0x39/0x22e] netlink_dump+0x39/0x22e
> > 
> > which lock already depends on the new lock.
> > 
> > the existing dependency chain (in reverse order) is:
> > 
> > -> #1 (nlk->cb_mutex){--..}:
> > [__lock_acquire+0xa02/0xbaf] __lock_acquire+0xa02/0xbaf
> > [lock_acquire+0x76/0x9d] lock_acquire+0x76/0x9d
> > [snd_mixer_oss:mutex_lock_nested+0xd5/0x67b] mutex_lock_nested+0xd5/0x274
> > [netlink_dump_start+0xbd/0x15a] netlink_dump_start+0xbd/0x15a
> > [genl_rcv_msg+0x9d/0x13a] genl_rcv_msg+0x9d/0x13a
> > [netlink_rcv_skb+0x30/0x75] netlink_rcv_skb+0x30/0x75
> > [genl_rcv+0x1e/0x2e] genl_rcv+0x1e/0x2e
> > [cfg80211:netlink_unicast+0x1c1/0x1867] netlink_unicast+0x1c1/0x293
> > [netlink_sendmsg+0x21f/0x22c] netlink_sendmsg+0x21f/0x22c
> > [sock_sendmsg+0xca/0xe1] sock_sendmsg+0xca/0xe1
> > [sys_sendmsg+0x14d/0x1a8] sys_sendmsg+0x14d/0x1a8
> > [sys_socketcall+0x163/0x17e] sys_socketcall+0x163/0x17e
> > [sysenter_past_esp+0x6d/0xc5] sysenter_past_esp+0x6d/0xc5
> >        [<ffffffff>] 0xffffffff
> > -> #0 (genl_mutex){--..}:
> > [__lock_acquire+0x929/0xbaf] __lock_acquire+0x929/0xbaf
> > [lock_acquire+0x76/0x9d] lock_acquire+0x76/0x9d
> > [snd_mixer_oss:mutex_lock_nested+0xd5/0x67b] mutex_lock_nested+0xd5/0x274
> > [ctrl_dumpfamily+0x37/0xda] ctrl_dumpfamily+0x37/0xda
> > [netlink_dump+0x51/0x22e] netlink_dump+0x51/0x22e
> > [netlink_recvmsg+0x156/0x203] netlink_recvmsg+0x156/0x203
> > [sock_recvmsg+0xd1/0xe9] sock_recvmsg+0xd1/0xe9
> > [sys_recvmsg+0xf2/0x17f] sys_recvmsg+0xf2/0x17f
> > [sys_socketcall+0x16f/0x17e] sys_socketcall+0x16f/0x17e
> > [sysenter_past_esp+0x6d/0xc5] sysenter_past_esp+0x6d/0xc5
> >        [<ffffffff>] 0xffffffff
> > 
> > other info that might help us debug this:
> > 
> > 1 lock held by iw/9417:
> >  #0: (nlk->cb_mutex){--..}, at: [netlink_dump+0x39/0x22e] netlink_dump+0x39/0x22e
> > 
> > stack backtrace:
> > Pid: 9417, comm: iw Not tainted 2.6.25-rc8-mm1 #15
> > [print_circular_bug_tail+0x5b/0x66] print_circular_bug_tail+0x5b/0x66
> > [print_circular_bug_header+0xa5/0xb0] ? print_circular_bug_header+0xa5/0xb0
> > [__lock_acquire+0x929/0xbaf] __lock_acquire+0x929/0xbaf
> > [lock_acquire+0x76/0x9d] lock_acquire+0x76/0x9d
> > [ctrl_dumpfamily+0x37/0xda] ? ctrl_dumpfamily+0x37/0xda
> > [snd_mixer_oss:mutex_lock_nested+0xd5/0x67b] mutex_lock_nested+0xd5/0x274
> > [ctrl_dumpfamily+0x37/0xda] ? ctrl_dumpfamily+0x37/0xda
> > [ctrl_dumpfamily+0x37/0xda] ? ctrl_dumpfamily+0x37/0xda
> > [ctrl_dumpfamily+0x37/0xda] ctrl_dumpfamily+0x37/0xda
> > [netlink_dump+0x51/0x22e] netlink_dump+0x51/0x22e
> > [mac80211:kfree_skb+0x40/0x45] ? kfree_skb+0x40/0x45
> > [netlink_recvmsg+0x156/0x203] netlink_recvmsg+0x156/0x203
> > [sock_sendmsg+0xca/0xe1] ? sock_sendmsg+0xca/0xe1
> > [sock_recvmsg+0xd1/0xe9] sock_recvmsg+0xd1/0xe9
> > [<c01313d9>] ? autoremove_wake_function+0x0/0x30
> > [snd_pcm_oss:copy_from_user+0x3b/0x236] ? copy_from_user+0x3b/0x5e
> > [verify_iovec+0x40/0x70] ? verify_iovec+0x40/0x70
> > [sys_recvmsg+0xf2/0x17f] sys_recvmsg+0xf2/0x17f
> > [snd_hda_intel:_spin_unlock_irqrestore+0x56/0x6c] ? _spin_unlock_irqrestore+0x56/0x6c
> > [paravirt_get_lazy_mode+0xe/0x1b] ? paravirt_get_lazy_mode+0xe/0x1b
> > [crypto_algapi:kunmap_atomic+0x9e/0x2e8e] ? kunmap_atomic+0x9e/0xbb
> > [handle_mm_fault+0x7aa/0x7bb] ? handle_mm_fault+0x7aa/0x7bb
> > [sys_socketcall+0x16f/0x17e] sys_socketcall+0x16f/0x17e
> > [processor:trace_hardirqs_on+0xf0/0x5d38] ? trace_hardirqs_on+0xf0/0x12c
> > [sysenter_past_esp+0x6d/0xc5] sysenter_past_esp+0x6d/0xc5
> > 
> 
> Yes, that looks like a problem in the core netlink code.  git-net contains
> several largeish changes to it..

The changes in git-net don't look locking related.  I suspect either:
wireless is calling netlink without holding rtnl_lock;
or more likely conditional locking ctrl_dumpfamily is confusing lockdep.

ctrl_dumpfamily only acquires genl_lock if one of the incoming parameters (chains_to_skip)
is non-zero. Not sure what the design reason is, Thomas could you add a comment?
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