On 13/10/20 15:21, Peter Zijlstra wrote: > On Tue, Oct 13, 2020 at 04:15:08PM +0200, Sebastian Andrzej Siewior wrote: >> On 2020-10-13 15:01:15 [+0100], Valentin Schneider wrote: >> > migrate_disable(); >> > set_cpus_allowed_ptr(current, {something excluding task_cpu(current)}); >> > affine_move_task(); <-- never returns >> > >> > Signed-off-by: Valentin Schneider <valentin.schnei...@arm.com> >> > --- >> > kernel/sched/core.c | 5 +++++ >> > 1 file changed, 5 insertions(+) >> > >> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> > index 4ccd1099adaa..7f4e38819de1 100644 >> > --- a/kernel/sched/core.c >> > +++ b/kernel/sched/core.c >> > @@ -2189,6 +2189,11 @@ static int __set_cpus_allowed_ptr(struct >> > task_struct *p, >> > if (!(flags & SCA_MIGRATE_ENABLE) && cpumask_equal(&p->cpus_mask, >> > new_mask)) >> > goto out; >> > >> > + if (p == current && >> > + is_migration_disabled(p) && >> > + !cpumask_test_cpu(task_cpu(p), new_mask)) >> > + ret = -EBUSY; >> > + >> >> This shouldn't happen, right? The function may sleep so it shouldn't be >> entered with disabled migration. A WARN_ON might spot the bad caller. > > So yeah, I like detecting the case but agree with bigeasy that an > additional WARN would make sense, lemme go add that.
Err, I've just realized that this will warn on migrate_enable() if there are pending affinity changes, since p->migration_disabled is cleared *after* the call to __set_cpus_allowed_ptr(). This wants: --- diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d503d6cb8350..e8156e3d3b4a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2266,7 +2266,8 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, if (!(flags & SCA_MIGRATE_ENABLE) && cpumask_equal(&p->cpus_mask, new_mask)) goto out; - if (WARN_ON_ONCE(p == current && + if (WARN_ON_ONCE(!(flags & SCA_MIGRATE_ENABLE) && + p == current && is_migration_disabled(p) && !cpumask_test_cpu(task_cpu(p), new_mask))) ret = -EBUSY; ---