Re: udev races with 'arch_register_cpu' to write 1 to /sys/devices/system/cpu/cpu1/online (which is not yet created).

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Apr 30, 2012 at 11:36:23AM -0400, Konrad Rzeszutek Wilk wrote:
> Hey Greg,
> 
> Hoping you can help with some guidance on how to fix this.
> 
> The issue is with CPU hotplug is that when a CPU goes up
> it calls 'arch_register_cpu' which eventually calls
> register_cpu. That function does these two things:
> 
> 251         error = device_register(&cpu->dev);
> 252         if (!error && cpu->hotpluggable)
> 253                 register_cpu_control(cpu);
> 
> and the device_register creates a nice little SysFS directory:
> 
> /sys/devices/system/cpu/cpu2/ which at line 251 has the 'add' attribute
> but no 'online' attribute. udev then tries to echo 1 to the 'online'
> and it we get:
> udevd-work[2421]: error opening ATTR{/sys/devices/system/cpu/cpu2/online} for writing: No such file or directory
> 
> Line 253 creates said 'online' and at that time udev [or the system admin]
> can write 1 to 'online' and the CPU goes up.
> 
> So .. any thoughts? Is there some way to inhibit from uevent being sent
> until line 253 has run?

Yes.