On Sat, 2017-06-17 at 10:14 +0200, Mike Galbraith wrote: > >... the RT workaround in futex.c induces > grumbling in nonrt builds with PREEMPT_COUNT enabled.
A trivial way to fix it up is to... futex: Fix migrate_disable/enable workaround for !PREEMPT_RT_FULL The imbalance fixed by aed0f50e58eb only exists for PREEMPT_RT_FULL, and creates for other PREEMPT_COUNT configs. Create/use _rt variants of migrate_disable/enable() which are compiled away when not needed. Signed-off-by: Mike Galbraith <[email protected]> Fixes: aed0f50e58eb ("futex: workaround migrate_disable/enable in different context") --- include/linux/preempt.h | 11 +++++++++++ kernel/futex.c | 8 ++++---- 2 files changed, 15 insertions(+), 4 deletions(-) --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -227,12 +227,21 @@ do { \ extern void migrate_disable(void); extern void migrate_enable(void); +#ifdef CONFIG_PREEMPT_RT_FULL +#define migrate_disable_rt() migrate_disable() +#define migrate_enable_rt() migrate_enable() +#else +static inline void migrate_disable_rt(void) { } +static inline void migrate_enable_rt(void) { } +#endif int __migrate_disabled(struct task_struct *p); #else #define migrate_disable() barrier() #define migrate_enable() barrier() +static inline void migrate_disable_rt(void) { } +static inline void migrate_enable_rt(void) { } static inline int __migrate_disabled(struct task_struct *p) { return 0; @@ -323,6 +332,8 @@ do { \ #define migrate_disable() barrier() #define migrate_enable() barrier() +static inline void migrate_disable_rt(void) { } +static inline void migrate_enable_rt(void) { } static inline int __migrate_disabled(struct task_struct *p) { --- a/kernel/futex.c +++ b/kernel/futex.c @@ -2690,12 +2690,12 @@ static int futex_lock_pi(u32 __user *uad * one migrate_disable() pending in the slow-path which is reversed * after the raw_spin_unlock_irq() where we leave the atomic context. */ - migrate_disable(); + migrate_disable_rt(); spin_unlock(q.lock_ptr); ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current); raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock); - migrate_enable(); + migrate_enable_rt(); if (ret) { if (ret == 1) @@ -2846,13 +2846,13 @@ static int futex_unlock_pi(u32 __user *u * won't undo the migrate_disable() which was issued when * locking hb->lock. */ - migrate_disable(); + migrate_disable_rt(); spin_unlock(&hb->lock); /* Drops pi_state->pi_mutex.wait_lock */ ret = wake_futex_pi(uaddr, uval, pi_state); - migrate_enable(); + migrate_enable_rt(); put_pi_state(pi_state);
