Date:	Sat, 15 Dec 2007 03:13:41 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Miles Lane" <miles.lane@...il.com>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	"Ingo Molnar" <mingo@...e.hu>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Subject: Re: 2.6.24-rc5-mm1 -- inconsistent {in-softirq-W} -> {softirq-on-R}
 usage.

On Fri, 14 Dec 2007 22:58:24 -0500 "Miles Lane" <miles.lane@...il.com> wrote:

> On Dec 14, 2007 6:36 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > On Fri, 14 Dec 2007 17:13:21 -0500
> > "Miles Lane" <miles.lane@...il.com> wrote:
> >
> >
> > > Sorry Andrew, I don't know who to forward this problem to.
> > >
> > > I tried running:  find /proc | xargs cat
> > > and got this:
> > >
> > > =================================
> > > [ INFO: inconsistent lock state ]
> > > 2.6.24-rc5-mm1 #26
> > > ---------------------------------
> > > inconsistent {in-softirq-W} -> {softirq-on-R} usage.
> > > cat/6944 [HC0[0]:SC0[0]:HE1:SE1] takes:
> > > BUG: unable to handle kernel paging request at virtual address 0f1eff0b
> > > printing ip: c01fe64d *pde = 00000000
> > > Oops: 0000 [#1] PREEMPT SMP
> > > last sysfs file: /sys/block/sda/sda3/stat
> > > Modules linked in: aes_generic i915 drm rfcomm l2cap bluetooth
> > > cpufreq_stats cpufreq_conservative cpufreq_performance sbs sbshc
> > > dm_crypt sbp2 parport_pc lp parport pcmcia arc4 ecb crypto_blkcipher
> > > cryptomgr crypto_algapi tifm_7xx1 tifm_core yenta_socket
> > > rsrc_nonstatic pcmcia_core iwl3945 iTCO_wdt iTCO_vendor_support
> > > watchdog_core watchdog_dev snd_hda_intel mac80211 snd_pcm_oss
> > > snd_mixer_oss cfg80211 snd_pcm sky2 snd_seq_dummy snd_seq_oss
> > > snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq snd_timer
> > > snd_seq_device snd soundcore snd_page_alloc shpchp pci_hotplug
> > > firewire_ohci firewire_core crc_itu_t ata_generic piix ide_core
> > >
> > > Pid: 6944, comm: cat Not tainted (2.6.24-rc5-mm1 #26)
> > > EIP: 0060:[<c01fe64d>] EFLAGS: 00210097 CPU: 0
> > > EIP is at strnlen+0x9/0x1c
> > > EAX: 0f1eff0b EBX: 0f1eff0b ECX: 0f1eff0b EDX: fffffffe
> > > ESI: c05b74f6 EDI: d6267d94 EBP: d6267cc8 ESP: d6267cc8
> > >  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
> > > Process cat (pid: 6944, ti=d6267000 task=d5a09000 task.ti=d6267000)
> > > Stack: d6267cfc c01fdd22 00000400 c05b74f4 00000001 c05b78f4 00000000 ffffffff
> > >        ffffffff c048f503 00000400 d5a09000 00000002 d6267d0c c01fdf41 d6267d94
> > >        db68c04a d6267d74 c012ae81 d6267d94 00000028 c05b89f7 00200046 00000000
> > > Call Trace:
> > >  [<c0108eb2>] show_trace_log_lvl+0x12/0x25
> > >  [<c0108f4f>] show_stack_log_lvl+0x8a/0x95
> > >  [<c0108fe4>] show_registers+0x8a/0x1bd
> > >  [<c010922f>] die+0x118/0x1dc
> > >  [<c03cf706>] do_page_fault+0x5a4/0x681
> > >  [<c03cdd72>] error_code+0x72/0x78
> > >  [<c01fdd22>] vsnprintf+0x277/0x40e
> > >  [<c01fdf41>] vscnprintf+0xe/0x1d
> > >  [<c012ae81>] vprintk+0xcb/0x2f3
> > >  [<c012b0be>] printk+0x15/0x17
> > >  [<c0145e55>] print_lock_name+0x4e/0xa2
> > >  [<c0146099>] print_lock+0xe/0x3a
> > >  [<c01464cf>] print_usage_bug+0xbc/0x117
> > >  [<c0146fb6>] mark_lock+0x2e7/0x3fe
> > >  [<c0147b9a>] __lock_acquire+0x498/0xbf4
> > >  [<c014836c>] lock_acquire+0x76/0x9d
> > >  [<c03cd6d2>] _read_lock+0x23/0x32
> > >  [<c03491ae>] sock_i_ino+0x14/0x30
> > >  [<c03c88ed>] packet_seq_show+0x22/0x75
> > >  [<c019b41a>] seq_read+0x19d/0x26f
> > >  [<c01b0ded>] proc_reg_read+0x60/0x74
> > >  [<c01854aa>] vfs_read+0x8a/0x106
> > >  [<c01858a8>] sys_read+0x3b/0x60
> > >  [<c0107cea>] sysenter_past_esp+0x6b/0xc1
> > >  =======================
> > > Code: 01 00 00 00 4f 89 fa 5f 89 d0 5d c3 55 85 c9 89 e5 57 89 c7 89
> > > d0 74 05 f2 ae 75 01 4f 89 f8 5f 5d c3 55 89 c1 89 e5 89 c8 eb 06 <80>
> > > 38 00 74 07 40 4a 83 fa ff 75 f4 29 c8 5d c3 90 90 90 55 83
> > > EIP: [<c01fe64d>] strnlen+0x9/0x1c SS:ESP 0068:d6267cc8
> > > note: cat[6944] exited with preempt_count 4
> >
> > I'd say you hit a networking locking bug and then when trying to report
> > that bug, lockdep crashed.
> >
> > The networking bug looks to be around sock_i_ino()'s taking of
> > sk_callback_lock with softirq's enabled.  Perhaps this will fix it.
> >
> > diff -puN net/core/sock.c~a net/core/sock.c
> > --- a/net/core/sock.c~a
> > +++ a/net/core/sock.c
> > @@ -1115,9 +1115,9 @@ int sock_i_uid(struct sock *sk)
> >  {
> >         int uid;
> >
> > -       read_lock(&sk->sk_callback_lock);
> > +       read_lock_bh(&sk->sk_callback_lock);
> >         uid = sk->sk_socket ? SOCK_INODE(sk->sk_socket)->i_uid : 0;
> > -       read_unlock(&sk->sk_callback_lock);
> > +       read_unlock_bh(&sk->sk_callback_lock);
> >         return uid;
> >  }
> >
> > @@ -1125,9 +1125,9 @@ unsigned long sock_i_ino(struct sock *sk
> >  {
> >         unsigned long ino;
> >
> > -       read_lock(&sk->sk_callback_lock);
> > +       read_lock_bh(&sk->sk_callback_lock);
> >         ino = sk->sk_socket ? SOCK_INODE(sk->sk_socket)->i_ino : 0;
> > -       read_unlock(&sk->sk_callback_lock);
> > +       read_unlock_bh(&sk->sk_callback_lock);
> >         return ino;
> >  }
> >
> > _
> >
> >
> 
> I applied the patch and then tried my test again.  This time my system
> locked up.
> Perhaps I should open a new thread for this, since the problem looks
> pretty different.
> 
> Dec 14 21:32:55 feargod kernel: process `cat' is using deprecated
> sysctl (syscall) net.ipv6.neigh.default.retrans_time; Use
> net.ipv6.neigh.default.retran
> s_time_ms instead.
> Dec 14 21:32:55 feargod kernel:
> Dec 14 21:32:55 feargod kernel: =====================================
> Dec 14 21:32:55 feargod kernel: [ BUG: bad unlock balance detected! ]
> Dec 14 21:32:55 feargod kernel: -------------------------------------
> Dec 14 21:32:55 feargod kernel: cat/6180 is trying to release lock
> (kkkkkkk�����H3��) at:
> Dec 14 21:32:55 feargod kernel: [packet_seq_stop+0xe/0x10]
> packet_seq_stop+0xe/0x10
> Dec 14 21:32:55 feargod kernel: but there are no more locks to release!
> Dec 14 21:32:55 feargod kernel:
> Dec 14 21:32:55 feargod kernel: other info that might help us debug this:
> Dec 14 21:32:55 feargod kernel: 2 locks held by cat/6180:
> Dec 14 21:32:55 feargod kernel:  #0:  (&p->lock){--..}, at:
> [crypto_algapi:seq_read+0x25/0x191c1] seq_read+0x25/0x26f
> Dec 14 21:32:55 feargod kernel:  #1:
> (&net->packet.sklist_lock){-.--}, at: [packet_seq_start+0x14/0x4d]
> packet_seq_start+0x14/0x4d

Bit of a mess.  We don't know whether lockdep is broken or if networking is
just feeding it garbage.  Or both.

My suspicion is that you've hit bad breakage in networking and lockdep just
isn't sufficiently robust to handle what it's being given.

Can you suggest a way in which others can reproduce this?

What happens if you run the same test with CONFIG_LOCKDEP=n?
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