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Date: Thu, 1 Dec 2016 18:08:00 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
linux-rt-users <linux-rt-users@...r.kernel.org>,
Steven Rostedt <rostedt@...dmis.org>
Subject: [ANNOUNCE] v4.8.11-rt7
Dear RT folks!
I'm pleased to announce the v4.8.11-rt7 patch set.
Changes since v4.8.11-rt6:
- A fix for a race in the futex/rtmutex code which was there since the
very beginning. Reported by David Daney, fixed Thomas Gleixner
- A fix for the kprobe code on ARM by Yang Shi.
- It is no longer possible to force an expedited RCU grace period on
-RT. We had one spot in the network where it was disabled on RT
due to high latencies it caused. Suggested by Luiz Capitulino and
patched by Julia Cartwright.
- Expedited RCU grace periods are now forced during boot which should
speed the boot process (even on -RT).
Known issues
- CPU hotplug got a little better but can deadlock.
The delta patch against 4.8.11-rt6 is appended below and can be found here:
https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.8/incr/patch-4.8.11-rt6-rt7.patch.xz
You can get this release via the git tree at:
git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git v4.8.11-rt7
The RT patch against 4.8.11 can be found here:
https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.8/patch-4.8.11-rt7.patch.xz
The split quilt queue is available at:
https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.8/patches-4.8.11-rt7.tar.xz
Sebastian
diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
index 69bda1a5707e..1f665acaa6a9 100644
--- a/arch/arm/kernel/patch.c
+++ b/arch/arm/kernel/patch.c
@@ -15,7 +15,7 @@ struct patch {
unsigned int insn;
};
-static DEFINE_SPINLOCK(patch_lock);
+static DEFINE_RAW_SPINLOCK(patch_lock);
static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
__acquires(&patch_lock)
@@ -32,7 +32,7 @@ static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
return addr;
if (flags)
- spin_lock_irqsave(&patch_lock, *flags);
+ raw_spin_lock_irqsave(&patch_lock, *flags);
else
__acquire(&patch_lock);
@@ -47,7 +47,7 @@ static void __kprobes patch_unmap(int fixmap, unsigned long *flags)
clear_fixmap(fixmap);
if (flags)
- spin_unlock_irqrestore(&patch_lock, *flags);
+ raw_spin_unlock_irqrestore(&patch_lock, *flags);
else
__release(&patch_lock);
}
diff --git a/init/Kconfig b/init/Kconfig
index b6c9166d878a..fe51bd3bbc61 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -771,19 +771,6 @@ config RCU_NOCB_CPU_ALL
endchoice
-config RCU_EXPEDITE_BOOT
- bool
- default n
- help
- This option enables expedited grace periods at boot time,
- as if rcu_expedite_gp() had been invoked early in boot.
- The corresponding rcu_unexpedite_gp() is invoked from
- rcu_end_inkernel_boot(), which is intended to be invoked
- at the end of the kernel-only boot sequence, just before
- init is exec'ed.
-
- Accept the default if unsure.
-
endmenu # "RCU Subsystem"
config BUILD_BIN2C
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 2576f7ccf8e2..6f2ded470af1 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -71,8 +71,72 @@ static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
{
- if (!rt_mutex_has_waiters(lock))
- clear_rt_mutex_waiters(lock);
+ unsigned long owner, *p = (unsigned long *) &lock->owner;
+
+ if (rt_mutex_has_waiters(lock))
+ return;
+
+ /*
+ * The rbtree has no waiters enqueued, now make sure that the
+ * lock->owner still has the waiters bit set, otherwise the
+ * following can happen:
+ *
+ * CPU 0 CPU 1 CPU2
+ * l->owner=T1
+ * rt_mutex_lock(l)
+ * lock(l->lock)
+ * l->owner = T1 | HAS_WAITERS;
+ * enqueue(T2)
+ * boost()
+ * unlock(l->lock)
+ * block()
+ *
+ * rt_mutex_lock(l)
+ * lock(l->lock)
+ * l->owner = T1 | HAS_WAITERS;
+ * enqueue(T3)
+ * boost()
+ * unlock(l->lock)
+ * block()
+ * signal(->T2) signal(->T3)
+ * lock(l->lock)
+ * dequeue(T2)
+ * deboost()
+ * unlock(l->lock)
+ * lock(l->lock)
+ * dequeue(T3)
+ * ==> wait list is empty
+ * deboost()
+ * unlock(l->lock)
+ * lock(l->lock)
+ * fixup_rt_mutex_waiters()
+ * if (wait_list_empty(l) {
+ * l->owner = owner
+ * owner = l->owner & ~HAS_WAITERS;
+ * ==> l->owner = T1
+ * }
+ * lock(l->lock)
+ * rt_mutex_unlock(l) fixup_rt_mutex_waiters()
+ * if (wait_list_empty(l) {
+ * owner = l->owner & ~HAS_WAITERS;
+ * cmpxchg(l->owner, T1, NULL)
+ * ===> Success (l->owner = NULL)
+ *
+ * l->owner = owner
+ * ==> l->owner = T1
+ * }
+ *
+ * With the check for the waiter bit in place T3 on CPU2 will not
+ * overwrite. All tasks fiddling with the waiters bit are
+ * serialized by l->lock, so nothing else can modify the waiters
+ * bit. If the bit is set then nothing can change l->owner either
+ * so the simple RMW is safe. The cmpxchg() will simply fail if it
+ * happens in the middle of the RMW because the waiters bit is
+ * still set.
+ */
+ owner = READ_ONCE(*p);
+ if (owner & RT_MUTEX_HAS_WAITERS)
+ WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
}
static int rt_mutex_real_waiter(struct rt_mutex_waiter *waiter)
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index b40d3468ba4e..2025ad12d241 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -63,7 +63,7 @@ MODULE_ALIAS("rcupdate");
#ifndef CONFIG_TINY_RCU
module_param(rcu_expedited, int, 0);
module_param(rcu_normal, int, 0);
-static int rcu_normal_after_boot;
+static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT_FULL);
module_param(rcu_normal_after_boot, int, 0);
#endif /* #ifndef CONFIG_TINY_RCU */
@@ -130,8 +130,7 @@ bool rcu_gp_is_normal(void)
}
EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
-static atomic_t rcu_expedited_nesting =
- ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0);
+static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
/*
* Should normal grace-period primitives be expedited? Intended for
@@ -179,8 +178,7 @@ EXPORT_SYMBOL_GPL(rcu_unexpedite_gp);
*/
void rcu_end_inkernel_boot(void)
{
- if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT))
- rcu_unexpedite_gp();
+ rcu_unexpedite_gp();
if (rcu_normal_after_boot)
WRITE_ONCE(rcu_normal, 1);
}
diff --git a/localversion-rt b/localversion-rt
index 8fc605d80667..045478966e9f 100644
--- a/localversion-rt
+++ b/localversion-rt
@@ -1 +1 @@
--rt6
+-rt7
diff --git a/net/core/dev.c b/net/core/dev.c
index a35311052845..4ba0c36fc389 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7766,7 +7766,7 @@ EXPORT_SYMBOL(free_netdev);
void synchronize_net(void)
{
might_sleep();
- if (rtnl_is_locked() && !IS_ENABLED(CONFIG_PREEMPT_RT_FULL))
+ if (rtnl_is_locked())
synchronize_rcu_expedited();
else
synchronize_rcu();
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