On 07/07/2009 09:15 PM, Peter Zijlstra wrote:
On Tue, 2009-07-07 at 15:06 -0300, Marcelo Tosatti wrote:
KVM guests with CONFIG_LOCKDEP=y trigger the following warning:
BUG: MAX_LOCK_DEPTH too low!
turning off the locking correctness validator.
Pid: 4624, comm: qemu-system-x86 Not tainted 2.6.31-rc2-03981-g3abaf21
#32
Call Trace:
[<ffffffff81068bab>] __lock_acquire+0x1559/0x15fc
[<ffffffff810be4d9>] ? mm_take_all_locks+0x99/0x109
[<ffffffff810be4d9>] ? mm_take_all_locks+0x99/0x109
[<ffffffff81068d3c>] lock_acquire+0xee/0x112
[<ffffffff810be516>] ? mm_take_all_locks+0xd6/0x109
[<ffffffff81402596>] ? _spin_lock_nest_lock+0x20/0x50
[<ffffffff814025b7>] _spin_lock_nest_lock+0x41/0x50
[<ffffffff810be516>] ? mm_take_all_locks+0xd6/0x109
[<ffffffff810be516>] mm_take_all_locks+0xd6/0x109
[<ffffffff810d0f76>] do_mmu_notifier_register+0xd4/0x199
[<ffffffff810d1060>] mmu_notifier_register+0x13/0x15
[<ffffffffa0107f16>] kvm_dev_ioctl+0x13f/0x30e [kvm]
[<ffffffff810e6a3a>] vfs_ioctl+0x2f/0x7d
[<ffffffff810e6fb7>] do_vfs_ioctl+0x4af/0x4ec
[<ffffffff814030b4>] ? error_exit+0x94/0xb0
[<ffffffff81401f92>] ? trace_hardirqs_off_thunk+0x3a/0x3c
[<ffffffff8100bc2d>] ? retint_swapgs+0xe/0x13
[<ffffffff810e703b>] sys_ioctl+0x47/0x6a
[<ffffffff811d849c>] ? __up_read+0x1a/0x85
[<ffffffff8100b1db>] system_call_fastpath+0x16/0x1b
Since mm_take_all_locks takes a gazillion locks.
Is there any way around this other than completly shutting down lockdep?
When we created this the promise was that kvm would only do this on a
fresh mm with only a few vmas, has that changed
The number of vmas did increase, but not materially. We do link with
more shared libraries though.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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