On 12/08/20 13:28, 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. > > 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); Why is it safe to return that for cpuset v2? task_cs(tsk)->cpus_allowed is the original user configured settings of the cpuset.cpus; which could have empty intersection with task_cpu_possible_mask(), no? do_set_cpus_allowed() will call set_cpus_allowed_common() which will end up copying the mask as-is. So unless I missed something there's a risk a 32bit task ends up having a 64bit only cpu_mask when using cpuset v2. Thanks -- Qais Yousef > rcu_read_unlock(); > > /* > -- > 2.29.2.576.ga3fc446d84-goog >