| From: Thomas Gleixner <tglx@linutronix.de> |
| Date: Wed, 8 Mar 2017 14:23:35 +0100 |
| Subject: [PATCH] futex: workaround migrate_disable/enable in different context |
| |
| migrate_disable()/migrate_enable() takes a different path in atomic() vs |
| !atomic() context. These little hacks ensure that we don't underflow / overflow |
| the migrate code counts properly while we lock the hb lockwith interrupts |
| enabled and unlock it with interrupts disabled. |
| |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> |
| --- |
| kernel/futex.c | 20 ++++++++++++++++++++ |
| 1 file changed, 20 insertions(+) |
| |
| --- a/kernel/futex.c |
| +++ b/kernel/futex.c |
| @@ -2671,9 +2671,18 @@ static int futex_lock_pi(u32 __user *uad |
| * lock handoff sequence. |
| */ |
| raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock); |
| + /* |
| + * the migrate_disable() here disables migration in the in_atomic() fast |
| + * path which is enabled again in the following spin_unlock(). We have |
| + * 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(); |
| + |
| 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(); |
| |
| if (ret) { |
| if (ret == 1) |
| @@ -2817,10 +2826,21 @@ static int futex_unlock_pi(u32 __user *u |
| * observed. |
| */ |
| raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
| + /* |
| + * Magic trickery for now to make the RT migrate disable |
| + * logic happy. The following spin_unlock() happens with |
| + * interrupts disabled so the internal migrate_enable() |
| + * won't undo the migrate_disable() which was issued when |
| + * locking hb->lock. |
| + */ |
| + migrate_disable(); |
| spin_unlock(&hb->lock); |
| |
| + /* Drops pi_state->pi_mutex.wait_lock */ |
| ret = wake_futex_pi(uaddr, uval, pi_state); |
| |
| + migrate_enable(); |
| + |
| put_pi_state(pi_state); |
| |
| /* |
