Re: [Xen-devel] [BUGFIX PATCH for-4.13] sched: fix dom0less boot with the null scheduler

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

> On Nov 6, 2019, at 3:58 PM, Dario Faggioli <dfaggioli@xxxxxxxx> wrote:
> 
> In a dom0less configuration, if the null scheduler is used, the system
> may fail to boot, because the loop in null_unit_wake() never exits.
> 
> Bisection showed that this behavior occurs since commit d545f1d6 ("xen:
> sched: deal with vCPUs being or becoming online or offline") but the
> real problem is that, in this case, pick_res() always return the same
> CPU.
> 
> Fix this by only deal with the simple case, i.e., the vCPU that is
> coming online can be assigned to a sched. resource right away, in
> null_unit_wake().
> 
> If it can't, just add it to the waitqueue, and we will deal with it in
> null_schedule(), being careful about not racing with vcpu_wake().
> 
> Reported-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Signed-off-by: Dario Faggioli <dfaggioli@xxxxxxxx>
> Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>

With one minor nit…

> +     * and it's previous resource is free (and affinities match), we can just

its (no ‘).  I’ll change this on check-in.

 -George

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