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

[Jürgen Groß <jgross@xxxxxxx>]

On 06.11.19 16:58, Dario Faggioli 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>
Release-acked-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

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