Re: [Qemu-devel] [PATCH v4 3/6] KVM: Initialize irqfd from kvm_init().

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Tue, 02 Apr 2013 20:40:53 -0400
Sasha Levin <sasha.levin@oracle.com> wrote:

> On 02/28/2013 04:22 AM, Cornelia Huck wrote:
> > Currently, eventfd introduces module_init/module_exit functions
> > to initialize/cleanup the irqfd workqueue. This only works, however,
> > if no other module_init/module_exit functions are built into the
> > same module.
> > 
> > Let's just move the initialization and cleanup to kvm_init and kvm_exit.
> > This way, it is also clearer where kvm startup may fail.
> > 
> > Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> 
> I'm seeing this during boot:
> 
> [    6.763302] ------------[ cut here ]------------
> [    6.763763] WARNING: at kernel/workqueue.c:4204 destroy_workqueue+0x1df/0x3d0()
> [    6.764507] Modules linked in:
> [    6.764792] Pid: 1, comm: swapper/0 Tainted: G        W    3.9.0-rc5-next-20130402-sasha-00015-g3522ec5 #324
> [    6.765654] Call Trace:
> [    6.765875]  [<ffffffff811074fb>] warn_slowpath_common+0x8b/0xc0
> [    6.766436]  [<ffffffff81107545>] warn_slowpath_null+0x15/0x20
> [    6.766947]  [<ffffffff8112ca7f>] destroy_workqueue+0x1df/0x3d0
> [    6.768631]  [<ffffffff8100d880>] kvm_irqfd_exit+0x10/0x20
> [    6.770000]  [<ffffffff81004dbb>] kvm_init+0x2ab/0x310
> [    6.770607]  [<ffffffff86183dc0>] ? cpu_has_kvm_support+0x4d/0x4d
> [    6.771241]  [<ffffffff86183fb4>] vmx_init+0x1f4/0x437
> [    6.771709]  [<ffffffff86183dc0>] ? cpu_has_kvm_support+0x4d/0x4d
> [    6.772266]  [<ffffffff810020f2>] do_one_initcall+0xb2/0x1b0
> [    6.772995]  [<ffffffff86180021>] kernel_init_freeable+0x15d/0x1ef
> [    6.773857]  [<ffffffff8617f801>] ? loglevel+0x31/0x31
> [    6.774609]  [<ffffffff83d51230>] ? rest_init+0x140/0x140
> [    6.775551]  [<ffffffff83d51239>] kernel_init+0x9/0xf0
> [    6.776162]  [<ffffffff83dbf37c>] ret_from_fork+0x7c/0xb0
> [    6.776662]  [<ffffffff83d51230>] ? rest_init+0x140/0x140
> [    6.777241] ---[ end trace 10bba684ced4346a ]---
> 
> And I think it has something to do with this patch.

What this patch does is move initialization of the workqueue - the code
called should be indentical.

The workqueue created/destroyed should not have been touched (no irqfds
yet), but the new workqueue code seems to encounter something
unexpected.

I'd expect destroy_workqueue() to be callable after a successful
create_singlethread_workqueue(). Tejun?

> 
> 
> Thanks,
> Sasha
>