On Thu, Jul 05, 2018 at 05:50:34PM +0200, Sebastian Andrzej Siewior wrote: > migrate_disable() does nothing !SMP && !RT. This is bad for two reasons: > - The futex code relies on the fact migrate_disable() is part of spin_lock(). > There is a workaround for the !in_atomic() case in migrate_disable() which > work-arounds the different ordering (non-atomic lock and atomic unlock). > > - we have a few instances where preempt_disable() is replaced with > migrate_disable(). > > For both cases it is bad if migrate_disable() ends up as barrier() instead of > preempt_disable(). Let migrate_disable() fallback to preempt_disable(). > > Cc: [email protected] > Reported-by: [email protected] > Signed-off-by: Sebastian Andrzej Siewior <[email protected]> > --- > include/linux/preempt.h | 4 ++-- > kernel/sched/core.c | 2 ++ > 2 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/include/linux/preempt.h b/include/linux/preempt.h > index 043e431a7e8e..d46688d521e6 100644 > --- a/include/linux/preempt.h > +++ b/include/linux/preempt.h > @@ -241,8 +241,8 @@ static inline int __migrate_disabled(struct task_struct > *p) > } > > #else > -#define migrate_disable() barrier() > -#define migrate_enable() barrier() > +#define migrate_disable() preempt_disable() > +#define migrate_enable() preempt_enable() > static inline int __migrate_disabled(struct task_struct *p) > { > return 0; > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index ac3fb8495bd5..626a62218518 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -7326,6 +7326,7 @@ void migrate_disable(void) > #endif > > p->migrate_disable++; > + preempt_disable(); > } > EXPORT_SYMBOL(migrate_disable); > > @@ -7349,6 +7350,7 @@ void migrate_enable(void) > > WARN_ON_ONCE(p->migrate_disable <= 0); > p->migrate_disable--; > + preempt_enable(); > } > EXPORT_SYMBOL(migrate_enable); > #endif > -- > 2.18.0
Hi Sebastian, I just verified that this fix does not work for my mix of config options (smp && preempt && !rt). Regards, Joe
