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

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Date:	Fri, 10 May 2013 18:34:34 +0200
From:	Igor Mammedov <imammedo@...hat.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org
Subject: Re: udev races with 'arch_register_cpu' to write 1 to /sys/devices/system/cpu/cpu1/online (which is not yet created)

>On Mon, Apr 30, 2012 at 11:51:49AM -0400, Greg KH wrote:
>> On Mon, Apr 30, 2012 at 11:50:18AM -0400, Greg KH wrote:
>> > 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.
>> 
>> Oh, I imagine you want to know _how_ to do it too, right?  (sorry, I
>> couldn't resist...)
>
>Heh.
>> 
>> Make this a default attribute of the cpu device, and then it will be
>> created by the driver core before the uevent is sent to userspace.
>> That's what you are supposed to do in the first place, adding files "by
>> hand" is wrong, for this very reason.
>
>OK, will prep up a patch shortly.

Hello Konrad,

Is there a posted/accepted patch or idea was dropped?


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