On 11/24/20 15:50, Will Deacon wrote: > If the scheduler cannot find an allowed CPU for a task, > cpuset_cpus_allowed_fallback() will widen the affinity to cpu_possible_mask > if cgroup v1 is in use. > > In preparation for allowing architectures to provide their own fallback > mask, just return early if we're not using cgroup v2 and allow > select_fallback_rq() to figure out the mask by itself. What about cpuset_attach()? When a task attaches to a new group its affinity could be reset to possible_cpu_mask if it moves to top_cpuset or the intersection of effective_cpus & cpu_online_mask. Probably handled with later patches. /me continue to look at the rest Okay so in patch 11 we make set_cpus_allowed_ptr() fail. cpuset_attach will just do WARN_ON_ONCE() and carry on. I think we can fix that by making sure cpuset_can_attach() will fail. Which can be done by fixing task_can_attach() to take into account the new arch task_cpu_possible_mask()? Thanks -- Qais Yousef > > Cc: Li Zefan <lizefan@xxxxxxxxxx> > Cc: Tejun Heo <tj@xxxxxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Reviewed-by: Quentin Perret <qperret@xxxxxxxxxx> > Signed-off-by: Will Deacon <will@xxxxxxxxxx> > --- > kernel/cgroup/cpuset.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 57b5b5d0a5fd..e970737c3ed2 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -3299,9 +3299,11 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) > > void cpuset_cpus_allowed_fallback(struct task_struct *tsk) > { > + if (!is_in_v2_mode()) > + return; /* select_fallback_rq will try harder */ > + > rcu_read_lock(); > - do_set_cpus_allowed(tsk, is_in_v2_mode() ? > - task_cs(tsk)->cpus_allowed : cpu_possible_mask); > + do_set_cpus_allowed(tsk, task_cs(tsk)->cpus_allowed); > rcu_read_unlock(); > > /* > -- > 2.29.2.454.gaff20da3a2-goog >