Re: [PATCH 3/2] padata: initialize usable masks to reflect offlined CPU

[Daniel Jordan]

On 8/21/19 11:51 PM, Herbert Xu wrote:
> On Mon, Aug 12, 2019 at 05:02:00PM -0400, Daniel Jordan wrote:
> > __padata_remove_cpu clears the offlined CPU from the usable masks after
> > padata_alloc_pd has initialized pd->cpu, which means pd->cpu could be
> > initialized to this CPU, causing padata to wait indefinitely for the
> > next job in padata_get_next.
> >
> > Make the usable masks reflect the offline CPU when they're established
> > in padata_setup_cpumasks so pd->cpu is initialized properly.
> >
> > Fixes: 6fc4dbcf0276 ("padata: Replace delayed timer with immediate workqueue in padata_reorder")
> > Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> > Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> > Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
> > Cc: linux-crypto@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > ---
> >
> > Hi, one more edge case.  All combinations of CPUs among
> > parallel_cpumask, serial_cpumask, and CPU hotplug have now been tested
> > in a 4-CPU VM, and an 8-CPU VM has run with random combinations of these
> > settings for over an hour.
> >
> >   kernel/padata.c | 18 ++++++++++++++----
> >   1 file changed, 14 insertions(+), 4 deletions(-)
>
> If we modify patch 2/2 by calling this after cpu_online_mask
> has been updated then this problem should go away because we
> can then remove the cpumask_clear_cpu calls.

Yep, agreed.