Re: [kvm.git & 2.6.37-rc1] KVM deadlock with CONFIG_PREEMPT host

[Jan Kiszka <jan.kiszka@siemens.com>]

Am 08.11.2010 10:18, Markus Trippelsdorf wrote:
> On Mon, Nov 08, 2010 at 10:04:00AM +0100, Jan Kiszka wrote:
>> Hi,
>>
>> I'm seeing lock-ups of the QEMU process on kvm.git as well as current
>> upstream kernels. This is a backtrace of the hanging VCPU thread:
>>
>> [<ffffffff810a27bc>] __stop_cpus+0x184/0x1a7
>> [<ffffffff810a286f>] try_stop_cpus+0x40/0x59
>> [<ffffffff8103a30c>] synchronize_sched_expedited+0x84/0x9d
>> [<ffffffff810715a3>] __synchronize_srcu+0x33/0x72
>> [<ffffffff810715f7>] synchronize_srcu_expedited+0x15/0x17
>> [<ffffffffa06602ae>] __kvm_set_memory_region+0x6a3/0x782 [kvm]
>> [<ffffffffa06603c4>] kvm_set_memory_region+0x37/0x50 [kvm]
>> [<ffffffffa0661c30>] kvm_vm_ioctl_set_memory_region+0x18/0x1a [kvm]
>> [<ffffffffa0661e5f>] kvm_vm_ioctl+0x22d/0x3b1 [kvm]
>> [<ffffffff81143c26>] do_vfs_ioctl+0x5a1/0x5e2
>> [<ffffffff81143cbd>] sys_ioctl+0x56/0x79
>> [<ffffffff81002df2>] system_call_fastpath+0x16/0x1b
>> [<ffffffffffffffff>] 0xffffffffffffffff
>>
>> This issue disappears when disabling CONFIG_PREEMPT on the host.
>> According to some rough bisecting, it was imported into kvm.git with
>> merge 146d3bb06b. Given that RCU is involved, I also tried
>> force-enabling non-preemptible CONFIG_TREE_RCU again, but that made no
>> difference as long as PREEMPT is on.
>>
>> Can anyone confirm this or does someone have an idea what goes wrong? Of
>> course, .config will be provided if required.
> 
> This patch should help (,it fixes the problem in my case):
> http://article.gmane.org/gmane.linux.kernel/1058018

Yeah, that works here as well.

Would be a nice-to-have in kvm.git until it's pull via the next upstream
merge. At least for me this bug triggers at every VM boot.

Jan

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