[PATCH RT 0/4] [ANNOUNCE] 3.4.42-rt57-rc1

[PATCH RT 0/4] [ANNOUNCE] 3.4.42-rt57-rc1

[Steven Rostedt]

Dear RT Folks,

This is the RT stable review cycle of patch 3.4.42-rt57-rc1.

Please scream at me if I messed something up. Please test the patches too.

The -rc release will be uploaded to kernel.org and will be deleted when
the final release is out. This is just a review release (or release candidate).

The pre-releases will not be pushed to the git repository, only the
final release is.

If all goes well, this patch will be converted to the next main release
on 5/7/2013.

Enjoy,

-- Steve


To build 3.4.42-rt57-rc1 directly, the following patches should be applied:

  http://www.kernel.org/pub/linux/kernel/v3.x/linux-3.4.tar.xz

  http://www.kernel.org/pub/linux/kernel/v3.x/patch-3.4.42.xz

  http://www.kernel.org/pub/linux/kernel/projects/rt/3.4/patch-3.4.42-rt57-rc1.patch.xz

You can also build from 3.4.42-rt56 by applying the incremental patch:

http://www.kernel.org/pub/linux/kernel/projects/rt/3.4/incr/patch-3.4.42-rt56-rt57-rc1.patch.xz


Changes from 3.4.42-rt56:

---


Eric Dumazet (1):
      tcp: force a dst refcount when prequeue packet

Steven Rostedt (2):
      x86/mce: Defer mce wakeups to threads for PREEMPT_RT
      swap: Use unique local lock name for swap_lock

Steven Rostedt (Red Hat) (1):
      Linux 3.4.42-rt57-rc1

----
 arch/x86/kernel/cpu/mcheck/mce.c |   78 +++++++++++++++++++++++++++++---------
 include/net/tcp.h                |    1 +
 localversion-rt                  |    2 +-
 mm/swap.c                        |   20 +++++-----
 4 files changed, 73 insertions(+), 28 deletions(-)

[PATCH RT 1/4] tcp: force a dst refcount when prequeue packet

[Steven Rostedt]

[-- Attachment #1: 0001-tcp-force-a-dst-refcount-when-prequeue-packet.patch --]
[-- Type: text/plain, Size: 901 bytes --]

From: Eric Dumazet <edumazet@google.com>

Before escaping RCU protected section and adding packet into
prequeue, make sure the dst is refcounted.

Cc: stable-rt@vger.kernel.org
Reported-by: Mike Galbraith <bitbucket@online.de>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/net/tcp.h |    1 +
 1 file changed, 1 insertion(+)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 2757a11..8376a6a 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -948,6 +948,7 @@ static inline int tcp_prequeue(struct sock *sk, struct sk_buff *skb)
 	if (sysctl_tcp_low_latency || !tp->ucopy.task)
 		return 0;
 
+	skb_dst_force(skb);
 	__skb_queue_tail(&tp->ucopy.prequeue, skb);
 	tp->ucopy.memory += skb->truesize;
 	if (tp->ucopy.memory > sk->sk_rcvbuf) {
-- 
1.7.10.4

[PATCH RT 2/4] x86/mce: Defer mce wakeups to threads for PREEMPT_RT

[Steven Rostedt]

[-- Attachment #1: 0002-x86-mce-Defer-mce-wakeups-to-threads-for-PREEMPT_RT.patch --]
[-- Type: text/plain, Size: 5471 bytes --]

From: Steven Rostedt <rostedt@goodmis.org>

We had a customer report a lockup on a 3.0-rt kernel that had the
following backtrace:

[ffff88107fca3e80] rt_spin_lock_slowlock at ffffffff81499113
[ffff88107fca3f40] rt_spin_lock at ffffffff81499a56
[ffff88107fca3f50] __wake_up at ffffffff81043379
[ffff88107fca3f80] mce_notify_irq at ffffffff81017328
[ffff88107fca3f90] intel_threshold_interrupt at ffffffff81019508
[ffff88107fca3fa0] smp_threshold_interrupt at ffffffff81019fc1
[ffff88107fca3fb0] threshold_interrupt at ffffffff814a1853

It actually bugged because the lock was taken by the same owner that
already had that lock. What happened was the thread that was setting
itself on a wait queue had the lock when an MCE triggered. The MCE
interrupt does a wake up on its wait list and grabs the same lock.

NOTE: THIS IS NOT A BUG ON MAINLINE

Sorry for yelling, but as I Cc'd mainline maintainers I want them to
know that this is an PREEMPT_RT bug only. I only Cc'd them for advice.

On PREEMPT_RT the wait queue locks are converted from normal
"spin_locks" into an rt_mutex (see the rt_spin_lock_slowlock above).
These are not to be taken by hard interrupt context. This usually isn't
a problem as most all interrupts in PREEMPT_RT are converted into
schedulable threads. Unfortunately that's not the case with the MCE irq.

As wait queue locks are notorious for long hold times, we can not
convert them to raw_spin_locks without causing issues with -rt. But
Thomas has created a "simple-wait" structure that uses raw spin locks
which may have been a good fit.

Unfortunately, wait queues are not the only issue, as the mce_notify_irq
also does a schedule_work(), which grabs the workqueue spin locks that
have the exact same issue.

Thus, this patch I'm proposing is to move the actual work of the MCE
interrupt into a helper thread that gets woken up on the MCE interrupt
and does the work in a schedulable context.

NOTE: THIS PATCH ONLY CHANGES THE BEHAVIOR WHEN PREEMPT_RT IS SET

Oops, sorry for yelling again, but I want to stress that I keep the same
behavior of mainline when PREEMPT_RT is not set. Thus, this only changes
the MCE behavior when PREEMPT_RT is configured.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[bigeasy@linutronix: make mce_notify_work() a proper prototype, use
		     kthread_run()]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 arch/x86/kernel/cpu/mcheck/mce.c |   78 +++++++++++++++++++++++++++++---------
 1 file changed, 61 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 91466f5..63c96f9 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -15,6 +15,7 @@
 #include <linux/rcupdate.h>
 #include <linux/kobject.h>
 #include <linux/uaccess.h>
+#include <linux/kthread.h>
 #include <linux/kdebug.h>
 #include <linux/kernel.h>
 #include <linux/percpu.h>
@@ -1293,6 +1294,63 @@ static void mce_do_trigger(struct work_struct *work)
 
 static DECLARE_WORK(mce_trigger_work, mce_do_trigger);
 
+static void __mce_notify_work(void)
+{
+	/* Not more than two messages every minute */
+	static DEFINE_RATELIMIT_STATE(ratelimit, 60*HZ, 2);
+
+	/* wake processes polling /dev/mcelog */
+	wake_up_interruptible(&mce_chrdev_wait);
+
+	/*
+	 * There is no risk of missing notifications because
+	 * work_pending is always cleared before the function is
+	 * executed.
+	 */
+	if (mce_helper[0] && !work_pending(&mce_trigger_work))
+		schedule_work(&mce_trigger_work);
+
+	if (__ratelimit(&ratelimit))
+		pr_info(HW_ERR "Machine check events logged\n");
+}
+
+#ifdef CONFIG_PREEMPT_RT_FULL
+struct task_struct *mce_notify_helper;
+
+static int mce_notify_helper_thread(void *unused)
+{
+	while (1) {
+		set_current_state(TASK_INTERRUPTIBLE);
+		schedule();
+		if (kthread_should_stop())
+			break;
+		__mce_notify_work();
+	}
+	return 0;
+}
+
+static int mce_notify_work_init(void)
+{
+	mce_notify_helper = kthread_run(mce_notify_helper_thread, NULL,
+					   "mce-notify");
+	if (!mce_notify_helper)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void mce_notify_work(void)
+{
+	wake_up_process(mce_notify_helper);
+}
+#else
+static void mce_notify_work(void)
+{
+	__mce_notify_work();
+}
+static inline int mce_notify_work_init(void) { return 0; }
+#endif
+
 /*
  * Notify the user(s) about new machine check events.
  * Can be called from interrupt context, but not from machine check/NMI
@@ -1300,24 +1358,8 @@ static DECLARE_WORK(mce_trigger_work, mce_do_trigger);
  */
 int mce_notify_irq(void)
 {
-	/* Not more than two messages every minute */
-	static DEFINE_RATELIMIT_STATE(ratelimit, 60*HZ, 2);
-
 	if (test_and_clear_bit(0, &mce_need_notify)) {
-		/* wake processes polling /dev/mcelog */
-		wake_up_interruptible(&mce_chrdev_wait);
-
-		/*
-		 * There is no risk of missing notifications because
-		 * work_pending is always cleared before the function is
-		 * executed.
-		 */
-		if (mce_helper[0] && !work_pending(&mce_trigger_work))
-			schedule_work(&mce_trigger_work);
-
-		if (__ratelimit(&ratelimit))
-			pr_info(HW_ERR "Machine check events logged\n");
-
+		mce_notify_work();
 		return 1;
 	}
 	return 0;
@@ -2295,6 +2337,8 @@ static __init int mcheck_init_device(void)
 	/* register character device /dev/mcelog */
 	misc_register(&mce_chrdev_device);
 
+	err = mce_notify_work_init();
+
 	return err;
 }
 device_initcall(mcheck_init_device);
-- 
1.7.10.4

[PATCH RT 3/4] swap: Use unique local lock name for swap_lock

[Steven Rostedt]

[-- Attachment #1: 0003-swap-Use-unique-local-lock-name-for-swap_lock.patch --]
[-- Type: text/plain, Size: 3519 bytes --]

From: Steven Rostedt <rostedt@goodmis.org>

>From lib/Kconfig.debug on CONFIG_FORCE_WEAK_PER_CPU:

----
s390 and alpha require percpu variables in modules to be
defined weak to work around addressing range issue which
puts the following two restrictions on percpu variable
definitions.

1. percpu symbols must be unique whether static or not
2. percpu variables can't be defined inside a function

To ensure that generic code follows the above rules, this
option forces all percpu variables to be defined as weak.
----

The addition of the local IRQ swap_lock in mm/swap.c broke this config
as the name "swap_lock" is used through out the kernel. Just do a "git
grep swap_lock" to see, and the new swap_lock is a local lock which
defines the swap_lock for per_cpu.

The fix was to rename swap_lock to swapvec_lock which keeps it unique.

Reported-by: Mike Galbraith <bitbucket@online.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 mm/swap.c |   20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 62dc70c..15c1c53 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -42,7 +42,7 @@ static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
 static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
 
 static DEFINE_LOCAL_IRQ_LOCK(rotate_lock);
-static DEFINE_LOCAL_IRQ_LOCK(swap_lock);
+static DEFINE_LOCAL_IRQ_LOCK(swapvec_lock);
 
 /*
  * This path almost never happens for VM activity - pages are normally
@@ -332,13 +332,13 @@ static void activate_page_drain(int cpu)
 void activate_page(struct page *page)
 {
 	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
-		struct pagevec *pvec = &get_locked_var(swap_lock,
+		struct pagevec *pvec = &get_locked_var(swapvec_lock,
 						       activate_page_pvecs);
 
 		page_cache_get(page);
 		if (!pagevec_add(pvec, page))
 			pagevec_lru_move_fn(pvec, __activate_page, NULL);
-		put_locked_var(swap_lock, activate_page_pvecs);
+		put_locked_var(swapvec_lock, activate_page_pvecs);
 	}
 }
 
@@ -378,12 +378,12 @@ EXPORT_SYMBOL(mark_page_accessed);
 
 void __lru_cache_add(struct page *page, enum lru_list lru)
 {
-	struct pagevec *pvec = &get_locked_var(swap_lock, lru_add_pvecs)[lru];
+	struct pagevec *pvec = &get_locked_var(swapvec_lock, lru_add_pvecs)[lru];
 
 	page_cache_get(page);
 	if (!pagevec_add(pvec, page))
 		__pagevec_lru_add(pvec, lru);
-	put_locked_var(swap_lock, lru_add_pvecs);
+	put_locked_var(swapvec_lock, lru_add_pvecs);
 }
 EXPORT_SYMBOL(__lru_cache_add);
 
@@ -548,19 +548,19 @@ void deactivate_page(struct page *page)
 		return;
 
 	if (likely(get_page_unless_zero(page))) {
-		struct pagevec *pvec = &get_locked_var(swap_lock,
+		struct pagevec *pvec = &get_locked_var(swapvec_lock,
 						       lru_deactivate_pvecs);
 
 		if (!pagevec_add(pvec, page))
 			pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
-		put_locked_var(swap_lock, lru_deactivate_pvecs);
+		put_locked_var(swapvec_lock, lru_deactivate_pvecs);
 	}
 }
 
 void lru_add_drain(void)
 {
-	lru_add_drain_cpu(local_lock_cpu(swap_lock));
-	local_unlock_cpu(swap_lock);
+	lru_add_drain_cpu(local_lock_cpu(swapvec_lock));
+	local_unlock_cpu(swapvec_lock);
 }
 
 static void lru_add_drain_per_cpu(struct work_struct *dummy)
@@ -771,7 +771,7 @@ EXPORT_SYMBOL(pagevec_lookup_tag);
 static int __init swap_init_locks(void)
 {
 	local_irq_lock_init(rotate_lock);
-	local_irq_lock_init(swap_lock);
+	local_irq_lock_init(swapvec_lock);
 	return 1;
 }
 early_initcall(swap_init_locks);
-- 
1.7.10.4

[PATCH RT 4/4] Linux 3.4.42-rt57-rc1

[Steven Rostedt]

[-- Attachment #1: 0004-Linux-3.4.42-rt57-rc1.patch --]
[-- Type: text/plain, Size: 299 bytes --]

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

---
 localversion-rt |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/localversion-rt b/localversion-rt
index fdb0f88..c12fc9d 100644
--- a/localversion-rt
+++ b/localversion-rt
@@ -1 +1 @@
--rt56
+-rt57-rc1
-- 
1.7.10.4