[ANNOUNCE] v4.16.18-rt12v4.16.18-rt12-patches

Dear RT folks!

I'm pleased to announce the v4.16.18-rt12 patch set.

Changes since v4.16.18-rt11:

  - Mark RCU's "rcu_iw" irqwork to be invoked in hardirq context as
    expected by RCU. Reported by John Ogness.

  - Drop the "is_special_task_state()" check from rtmutex's custom
    set_state function. This avoids a warning if the sleeping-lock code
    is restoring back to this "special" state.

  - If a kworker invokes schedule() it is possible that it wakes another
    kworker and invokes schedule() again. Try to avoid the second
    schedule(). Reported and patched by Daniel Bristot de Oliveira.

  - Enable XEN on ARM64. Iain Hunter reported that there are no problems
    with it so there is no reason to keep disabled.

Known issues
     - A warning triggered in "rcu_note_context_switch" originated from
       SyS_timer_gettime(). The issue was always there, it is now
       visible. Reported by Grygorii Strashko and Daniel Wagner.

The delta patch against v4.16.18-rt11 is appended below and can be found here:

     https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.16/incr/patch-4.16.18-rt11-rt12.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 v4.16.18-rt12

The RT patch against v4.16.18 can be found here:

    https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.16/older/patch-4.16.18-rt12.patch.xz

The split quilt queue is available at:

    https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.16/older/patches-4.16.18-rt12.tar.xz

Sebastian

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

7 files changed, 172 insertions, 8 deletions

diff --git a/patches/Revert-arm64-xen-Make-XEN-depend-on-RT.patch b/patches/Revert-arm64-xen-Make-XEN-depend-on-RT.patch
new file mode 100644
index 000000000000..e7bef17576a1
--- /dev/null
+++ b/patches/Revert-arm64-xen-Make-XEN-depend-on-RT.patch
@@ -0,0 +1,29 @@
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Date: Thu, 2 Aug 2018 17:11:01 +0200
+Subject: [PATCH] Revert "arm64/xen: Make XEN depend on !RT"
+
+Iain Hunter reported that there are no problems with it so there is no
+reason to keep it disabled.
+
+Reported-by: Iain Hunter <drhunter95@gmail.com>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ arch/arm64/Kconfig | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
+index d2370c7829451..3a6f0ae739d39 100644
+--- a/arch/arm64/Kconfig
++++ b/arch/arm64/Kconfig
+@@ -861,7 +861,7 @@ config XEN_DOM0
+ 
+ config XEN
+ 	bool "Xen guest support on ARM64"
+-	depends on ARM64 && OF && !PREEMPT_RT_FULL
++	depends on ARM64 && OF
+ 	select SWIOTLB_XEN
+ 	select PARAVIRT
+ 	help
+-- 
+2.18.0
+
diff --git a/patches/localversion.patch b/patches/localversion.patch
index 58842b503a27..12bd473a33f5 100644
--- a/patches/localversion.patch
+++ b/patches/localversion.patch
@@ -10,4 +10,4 @@ Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
 --- /dev/null
 +++ b/localversion-rt
 @@ -0,0 +1 @@
-+-rt11
++-rt12
diff --git a/patches/rcu-mark-rcu_iw_handler-as-IRQ_WORK_HARD_IRQ.patch b/patches/rcu-mark-rcu_iw_handler-as-IRQ_WORK_HARD_IRQ.patch
new file mode 100644
index 000000000000..075b37c20bb8
--- /dev/null
+++ b/patches/rcu-mark-rcu_iw_handler-as-IRQ_WORK_HARD_IRQ.patch
@@ -0,0 +1,31 @@
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Date: Mon, 30 Jul 2018 18:26:48 +0200
+Subject: [PATCH] rcu: mark rcu_iw_handler() as IRQ_WORK_HARD_IRQ
+
+RCU's rcu_iw irq-work (rcu_iw_handler()) acquires the raw spinlock
+rnp->lock without disabling interrupts. The lock is held normally with
+disabled interrupts for a short time.
+Mark irq-work as IRQ_WORK_HARD_IRQ so it is invoked in IRQ context like
+on !RT.
+
+Reported-by: John Ogness <john.ogness@linutronix.de>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ kernel/rcu/tree.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
+index 5a9c5abb17da..4fb983f4b9fd 100644
+--- a/kernel/rcu/tree.c
++++ b/kernel/rcu/tree.c
+@@ -1294,6 +1294,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
+ 		    !rdp->rcu_iw_pending && rdp->rcu_iw_gpnum != rnp->gpnum &&
+ 		    (rnp->ffmask & rdp->grpmask)) {
+ 			init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
++			rdp->rcu_iw.flags = IRQ_WORK_HARD_IRQ;
+ 			rdp->rcu_iw_pending = true;
+ 			rdp->rcu_iw_gpnum = rnp->gpnum;
+ 			irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
+-- 
+2.18.0
+
diff --git a/patches/sched-core-Avoid-__schedule-being-called-twice-in-a-.patch b/patches/sched-core-Avoid-__schedule-being-called-twice-in-a-.patch
new file mode 100644
index 000000000000..c9b4fb8ab55a
--- /dev/null
+++ b/patches/sched-core-Avoid-__schedule-being-called-twice-in-a-.patch
@@ -0,0 +1,52 @@
+From: Daniel Bristot de Oliveira <bristot@redhat.com>
+Date: Mon, 30 Jul 2018 15:00:00 +0200
+Subject: [PATCH] sched/core: Avoid __schedule() being called twice in a row
+
+If a worker invokes schedule() then we may have the call chain:
+ schedule()
+ -> sched_submit_work()
+    -> wq_worker_sleeping()
+       -> wake_up_worker()
+	  -> wake_up_process().
+
+The last wakeup may cause a schedule which is unnecessary because we are
+already in schedule() and do it anyway.
+
+Add a preempt_disable() + preempt_enable_no_resched() around
+wq_worker_sleeping() so the context switch could be delayed until
+__schedule().
+
+Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
+Cc: Clark Williams <williams@redhat.com>
+Cc: Tommaso Cucinotta <tommaso.cucinotta@sssup.it>
+Cc: Romulo da Silva de Oliveira <romulo.deoliveira@ufsc.br>
+Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Cc: Steven Rostedt <rostedt@goodmis.org>
+Cc: Thomas Gleixner <tglx@linutronix.de>
+Cc: Ingo Molnar <mingo@redhat.com>
+Cc: Peter Zijlstra <peterz@infradead.org>
+[bigeasy: rewrite changelog]
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ kernel/sched/core.c |    8 +++++++-
+ 1 file changed, 7 insertions(+), 1 deletion(-)
+
+--- a/kernel/sched/core.c
++++ b/kernel/sched/core.c
+@@ -3500,9 +3500,15 @@ static inline void sched_submit_work(str
+ 	/*
+ 	 * If a worker went to sleep, notify and ask workqueue whether
+ 	 * it wants to wake up a task to maintain concurrency.
++	 * As this function is called inside the schedule() context,
++	 * we disable preemption to avoid it calling schedule() again
++	 * in the possible wakeup of a kworker.
+ 	 */
+-	if (tsk->flags & PF_WQ_WORKER)
++	if (tsk->flags & PF_WQ_WORKER) {
++		preempt_disable();
+ 		wq_worker_sleeping(tsk);
++		preempt_enable_no_resched();
++	}
+ 
+ 	/*
+ 	 * If we are going to sleep and we have plugged IO queued,
diff --git a/patches/sched-drop-is_special_task_state-check-from-__set_cu.patch b/patches/sched-drop-is_special_task_state-check-from-__set_cu.patch
new file mode 100644
index 000000000000..3e028a304346
--- /dev/null
+++ b/patches/sched-drop-is_special_task_state-check-from-__set_cu.patch
@@ -0,0 +1,49 @@
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Date: Wed, 1 Aug 2018 10:33:05 +0200
+Subject: [PATCH] sched: drop is_special_task_state() check from
+ __set_current_state_no_track()
+
+The is_special_task_state() check in __set_current_state_no_track()
+has been wrongly placed. __set_current_state_no_track() is used in RT
+while a sleeping lock is acquired. It is used at the begin of the wait
+loop with TASK_UNINTERRUPTIBLE and while leaving it and restoring the
+original state. The latter part triggers the warning.
+
+Drop the special state check. This is only used within the sleeping lock
+implementation and the assignment happens while the PI lock is held.
+While at it, drop set_current_state_no_track() because it has no users.
+
+Cc: stable-rt@vger.kernel.org
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ include/linux/sched.h |   12 +-----------
+ 1 file changed, 1 insertion(+), 11 deletions(-)
+
+--- a/include/linux/sched.h
++++ b/include/linux/sched.h
+@@ -134,16 +134,7 @@ struct task_group;
+ 	} while (0)
+ 
+ #define __set_current_state_no_track(state_value)		\
+-	do {							\
+-		WARN_ON_ONCE(is_special_task_state(state_value));\
+-		current->state = (state_value);			\
+-	} while (0)
+-
+-#define set_current_state_no_track(state_value)			\
+-	do {							\
+-		WARN_ON_ONCE(is_special_task_state(state_value));\
+-		smp_store_mb(current->state, (state_value));	\
+-	} while (0)
++		current->state = (state_value);
+ 
+ #define set_special_state(state_value)					\
+ 	do {								\
+@@ -199,7 +190,6 @@ struct task_group;
+ 	smp_store_mb(current->state, (state_value))
+ 
+ #define __set_current_state_no_track(state_value)	__set_current_state(state_value)
+-#define set_current_state_no_track(state_value)		set_current_state(state_value)
+ 
+ /*
+  * set_special_state() should be used for those states when the blocking task
diff --git a/patches/series b/patches/series
index 134482620004..6a238889eedb 100644
--- a/patches/series
+++ b/patches/series
@@ -235,6 +235,7 @@ sched-disable-rt-group-sched-on-rt.patch
 net_disable_NET_RX_BUSY_POLL.patch
 arm-disable-NEON-in-kernel-mode.patch
 arm64-xen--Make-XEN-depend-on-non-rt.patch
+Revert-arm64-xen-Make-XEN-depend-on-RT.patch
 power-use-generic-rwsem-on-rt.patch
 powerpc-kvm-Disable-in-kernel-MPIC-emulation-for-PRE.patch
 power-disable-highmem-on-rt.patch
@@ -384,6 +385,7 @@ rtmutex_dont_include_rcu.patch
 rtmutex-Provide-rt_mutex_slowlock_locked.patch
 rtmutex-export-lockdep-less-version-of-rt_mutex-s-lo.patch
 rtmutex-add-sleeping-lock-implementation.patch
+sched-drop-is_special_task_state-check-from-__set_cu.patch
 rtmutex-add-mutex-implementation-based-on-rtmutex.patch
 rtmutex-add-rwsem-implementation-based-on-rtmutex.patch
 rtmutex-add-rwlock-implementation-based-on-rtmutex.patch
@@ -448,6 +450,7 @@ workqueue-use-rcu.patch
 workqueue-use-locallock.patch
 work-queue-work-around-irqsafe-timer-optimization.patch
 workqueue-distangle-from-rq-lock.patch
+sched-core-Avoid-__schedule-being-called-twice-in-a-.patch
 
 # DEBUGOBJECTS
 debugobjects-rt.patch
@@ -474,6 +477,7 @@ net-Have-__napi_schedule_irqoff-disable-interrupts-o.patch
 # irqwork
 irqwork-push_most_work_into_softirq_context.patch
 irqwork-Move-irq-safe-work-to-irq-context.patch
+rcu-mark-rcu_iw_handler-as-IRQ_WORK_HARD_IRQ.patch
 
 # CONSOLE. NEEDS more thought !!!
 printk-rt-aware.patch
diff --git a/patches/workqueue-prevent-deadlock-stall.patch b/patches/workqueue-prevent-deadlock-stall.patch
index b5c60e78ee99..d376f19ba75d 100644
--- a/patches/workqueue-prevent-deadlock-stall.patch
+++ b/patches/workqueue-prevent-deadlock-stall.patch
@@ -37,13 +37,13 @@ Cc: Richard Weinberger <richard.weinberger@gmail.com>
 Cc: Steven Rostedt <rostedt@goodmis.org>
 
 ---
- kernel/sched/core.c |    7 ++++--
+ kernel/sched/core.c |    6 +++--
  kernel/workqueue.c  |   60 ++++++++++++++++++++++++++++++++++++++++------------
- 2 files changed, 52 insertions(+), 15 deletions(-)
+ 2 files changed, 51 insertions(+), 15 deletions(-)
 
 --- a/kernel/sched/core.c
 +++ b/kernel/sched/core.c
-@@ -3550,9 +3550,8 @@ void __noreturn do_task_dead(void)
+@@ -3540,9 +3540,8 @@ void __noreturn do_task_dead(void)
  
  static inline void sched_submit_work(struct task_struct *tsk)
  {
@@ -54,11 +54,10 @@ Cc: Steven Rostedt <rostedt@goodmis.org>
  	/*
  	 * If a worker went to sleep, notify and ask workqueue whether
  	 * it wants to wake up a task to maintain concurrency.
-@@ -3560,6 +3559,10 @@ static inline void sched_submit_work(str
- 	if (tsk->flags & PF_WQ_WORKER)
- 		wq_worker_sleeping(tsk);
+@@ -3556,6 +3555,9 @@ static inline void sched_submit_work(str
+ 		preempt_enable_no_resched();
+ 	}
  
-+
 +	if (tsk_is_pi_blocked(tsk))
 +		return;
 +