Messages in this thread | | | Date | Mon, 13 May 2013 09:31:28 -0400 | From | Konrad Rzeszutek Wilk <> | Subject | 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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On Fri, May 10, 2013 at 06:34:34PM +0200, Igor Mammedov wrote: > >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?
Hey Igor,
CC-ing here Chuck here who is looking at that. My recollection (and Chuck please correct me if I am wrong) is that the idea Greg outlined won't work very well. The reason is that making 'online' an attribute of 'struct dev' means that: 1) A lot of SysFS attributes that have no notion of online/offline (say ISA bus) will now have. 2) The default action item (so function) to do something based on writting/reading from 'online' will have to be overridden by the driver using it. Which means another race - we can create an SysFS attribute but the default points to something that does nothing.
Chuck, does that sound right? > >
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