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 <efault@xxxxxx>
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);
--
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