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Date:	Mon, 8 Nov 2010 10:18:49 +0100
From:	Markus Trippelsdorf <>
To:	Jan Kiszka <>
Cc:	kvm <>,
	Linux Kernel Mailing List <>,
	Avi Kivity <>,
	Marcelo Tosatti <>,
	"Paul E. McKenney" <>
Subject: Re: [kvm.git & 2.6.37-rc1] KVM deadlock with CONFIG_PREEMPT host

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):
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