Re: WARN... Device 'cpu1' does not have a release() function, it is broken and must be fixed. when doing 'xl vcpu-set <guest_id> 1'

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jan 23, 2012 at 01:06:01PM -0500, Konrad Rzeszutek Wilk wrote:
> When I bring a CPU down in a guest (which should be the same as bringing a
> CPU down using the ACPI framework), I get this:
> 
> [   14.484206] SMP alternatives: switching to UP code
> [   14.514287] ------------[ cut here ]------------
> [   14.514318] WARNING: at /home/konrad/linux-linus/drivers/base/core.c:194 device_release+0x82/0x90()
> [   14.514354] Device 'cpu1' does not have a release() function, it is broken and must be fixed.
> [   14.514386] Modules linked in: radeon fbcon tileblit font ttm bitblit softcursor drm_kms_helper xen_blkfront xen_netfront xen_fbfront fb_sys_fops sysimgblt sysfillrect syscopyarea xen_kbdfront xenfs xen_privcmd
> [   14.514557] Pid: 22, comm: xenwatch Not tainted 3.3.0-rc1 #1
> [   14.514586] Call Trace:
> [   14.515094]  [<ffffffff810897fa>] warn_slowpath_common+0x7a/0xb0
> [   14.515094]  [<ffffffff810898d1>] warn_slowpath_fmt+0x41/0x50
> [   14.515094]  [<ffffffff813dea02>] device_release+0x82/0x90
> [   14.515094]  [<ffffffff812dfb85>] kobject_release+0x45/0x90
> [   14.515094]  [<ffffffff812dfa4c>] kobject_put+0x2c/0x60
> [   14.515094]  [<ffffffff813de6a2>] put_device+0x12/0x20
> [   14.515094]  [<ffffffff813df409>] device_unregister+0x19/0x20
> [   14.515094]  [<ffffffff813e4edf>] unregister_cpu+0x4f/0x80
> [   14.515094]  [<ffffffff81052c7c>] arch_unregister_cpu+0x1c/0x20
> [   14.515094]  [<ffffffff8137f787>] handle_vcpu_hotplug_event+0xc7/0xd0
> [   14.515094]  [<ffffffff8137b900>] xenwatch_thread+0xb0/0x180
> [   14.515094]  [<ffffffff810ad3f0>] ? wake_up_bit+0x40/0x40
> [   14.515094]  [<ffffffff8137b850>] ? split+0xf0/0xf0
> [   14.515094]  [<ffffffff810acd16>] kthread+0x96/0xa0
> [   14.515094]  [<ffffffff816151e4>] kernel_thread_helper+0x4/0x10
> [   14.515094]  [<ffffffff8160cc80>] ? retint_restore_args+0x5/0x6
> [   14.515094]  [<ffffffff816151e0>] ? gs_change+0x13/0x13
> [   14.515094] ---[ end trace 8f70af51a2e2611f ]---
> 
> Looking at "commit e032d80774315869aa2285b217fdbbfed86c0b49
> Author: Greg Kroah-Hartman <gregkh@suse.de>
> Date:   Mon Jan 16 14:40:28 2012 -0800
> 
>     mce: fix warning messages about static struct mce_device
> "
> 
> it looks like the corret fix is to make the 'cpu_devices' in
> arch/x86/kernel/topology.c to be changed to be more dynamic
> (or perhaps have an empty release function)?
> 
> Is anybody else hitting this with ACPI CPU hot-unplug? Or do I have
> the privilige of being the first? Oh, I hadn't done a full bisection
> but v3.2 does not have this.

Does the patch below solve the problem for you?

thanks,

greg k-h


diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index db87e78..23f2c4c 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -208,6 +208,25 @@ static ssize_t print_cpus_offline(struct device *dev,
 }
 static DEVICE_ATTR(offline, 0444, print_cpus_offline, NULL);
 
+static void cpu_device_release(struct device *dev)
+{
+	/*
+	 * This is an empty function to prevent the driver core from spitting a
+	 * warning at us.  Yes, I know this is directly opposite of what the
+	 * documentation for the driver core and kobjects say, and the author
+	 * of this code has already been publically ridiculed for doing
+	 * something as foolish as this.  However, at this point in time, it is
+	 * the only way to handle the issue of statically allocated cpu
+	 * devices.  The different architectures will have their cpu device
+	 * code reworked to properly handle this in the near future, so this
+	 * function will then be changed to correctly free up the memory held
+	 * by the cpu device.
+	 *
+	 * Never copy this way of doing things, or you too will be made fun of
+	 * on the linux-kerenl list, you have been warned.
+	 */
+}
+
 /*
  * register_cpu - Setup a sysfs device for a CPU.
  * @cpu - cpu->hotpluggable field set to 1 will generate a control file in
@@ -223,6 +242,7 @@ int __cpuinit register_cpu(struct cpu *cpu, int num)
 	cpu->node_id = cpu_to_node(num);
 	cpu->dev.id = num;
 	cpu->dev.bus = &cpu_subsys;
+	cpu->dev.release = cpu_device_release;
 	error = device_register(&cpu->dev);
 	if (!error && cpu->hotpluggable)
 		register_cpu_control(cpu);