From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: Lock warning traceback
Date: Tue, 29 Sep 2009 13:50:42 -0300
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Cc: kvm@vger.kernel.org
To: Priit Laes <plaes@plaes.org>
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On Tue, Sep 29, 2009 at 08:56:24AM +0300, Priit Laes wrote:
> Hi!
> 
> I've been getting some locking-related warning when I fire up a KVM
> machine. This has been popping up since a 2.6.30 kernel:
> 
> [snip]
> [119206.978058] BUG: MAX_LOCK_DEPTH too low!
> [119206.978062] turning off the locking correctness validator.
> [119206.978067] Pid: 9510, comm: kvm Not tainted 2.6.31 #44
> [119206.978071] Call Trace:
> [119206.978080]  [<ffffffff8108e4a9>] __lock_acquire+0x94c/0x974
> [119206.978086]  [<ffffffff8108e59d>] lock_acquire+0xcc/0xe9
> [119206.978092]  [<ffffffff810e106f>] ? mm_take_all_locks+0xd9/0x110
> [119206.978099]  [<ffffffff814af652>] ? mutex_lock_nested+0x23b/0x24a
> [119206.978104]  [<ffffffff810e0fd0>] ? mm_take_all_locks+0x3a/0x110
> [119206.978109]  [<ffffffff814b05b9>] _spin_lock_nest_lock+0x2c/0x3b
> [119206.978114]  [<ffffffff810e106f>] ? mm_take_all_locks+0xd9/0x110
> [119206.978119]  [<ffffffff810e106f>] mm_take_all_locks+0xd9/0x110
> [119206.978125]  [<ffffffff810efe83>] do_mmu_notifier_register
> +0xa8/0x16a
> [119206.978130]  [<ffffffff810eff60>] mmu_notifier_register+0xe/0x10
> [119206.978136]  [<ffffffff8100daba>] kvm_dev_ioctl+0x136/0x2ed
> [119206.978142]  [<ffffffff811061f9>] vfs_ioctl+0x1d/0x82
> [119206.978147]  [<ffffffff81106730>] do_vfs_ioctl+0x45b/0x4a1
> [119206.978153]  [<ffffffff811fdb78>] ? __up_read+0x9a/0xa2
> [119206.978158]  [<ffffffff8108287b>] ? up_read+0x26/0x2a
> [119206.978163]  [<ffffffff811067b8>] sys_ioctl+0x42/0x65
> [119206.978169]  [<ffffffff810329eb>] system_call_fastpath+0x16/0x1b
> [119216.471426] kvm: emulating exchange as write
> [/snip]
> 
> Although, this does not seem to be critical as my guest op-system seems
> to be working fine...

This should fixed in recent kernels.