[libvirt] [PATCH] qemu: Refresh capabilities when creating resctrl allocation

[Martin Kletzander]

On Fri, Feb 02, 2018 at 02:29:03PM +0100, Peter Krempa wrote:
>On Fri, Feb 02, 2018 at 12:44:03 +0100, Martin Kletzander wrote:
>> Since one of the things in capabilities (info from resctrl updated with data
>> about caches) can be change on the system by remounting the /sys/fs/resctrl with
>> different options, the capabilities need to be refreshed.  There is a better fix
>> in the works, but it's going to be way bigger than this (hence the XXX note
>> there), so for the time being let's workaround this.  And in order not to slow
>> down the domain starting, only get the capabilities if there are any cachetunes.
>>
>> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1540780
>
>This BZ describes a crash if the filesystem is remounted, but you are
>attempting to fix this not by fixing the code that crashed but by
>re-loading the information if possibly somebody remounted it.
>
>This does not seem to be the correct fix since you still have a race
>window, where the options can be changed after the refresh is executed
>and prior to using them in the code where it actually crashed.

Yeah, I'm looking at that as well.  It will need a restructuring (moving some
conf code to util - it'll also look nicer), but fix for exactly what is
happening here is enough for now.

Martin
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