blob: 939689090f2986336df713dcdc4c6dedee7eb59a [file] [log] [blame]
From 562e9207a8ef3f7c67de7312659f26f891af8473 Mon Sep 17 00:00:00 2001
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(+)
diff --git a/kernel/futex.c b/kernel/futex.c
index d4ec1a1404fc..f5b21fd753a9 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2682,9 +2682,18 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
* 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)
@@ -2828,11 +2837,21 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
* 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);
/*
--
2.15.0