[PATCH RT 0/9] Linux 5.10.78-rt56-rc1.

[PATCH RT 0/9] Linux 5.10.78-rt56-rc1.

[Steven Rostedt]

Dear RT Folks,

This is the RT stable review cycle of patch 5.10.78-rt56-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 11/18/2021.

Enjoy,

-- Steve


To build 5.10.78-rt56-rc1 directly, the following patches should be applied:

  http://www.kernel.org/pub/linux/kernel/v5.x/linux-5.10.tar.xz

  http://www.kernel.org/pub/linux/kernel/v5.x/patch-5.10.78.xz

  http://www.kernel.org/pub/linux/kernel/projects/rt/5.10/patch-5.10.78-rt56-rc1.patch.xz

You can also build from 5.10.78-rt55 by applying the incremental patch:

http://www.kernel.org/pub/linux/kernel/projects/rt/5.10/incr/patch-5.10.78-rt55-rt56-rc1.patch.xz


Changes from 5.10.78-rt55:

---


Mike Galbraith (1):
      mm, zsmalloc: Convert zsmalloc_handle.lock to spinlock_t

Sebastian Andrzej Siewior (7):
      sched: Fix get_push_task() vs migrate_disable()
      sched: Switch wait_task_inactive to HRTIMER_MODE_REL_HARD
      preempt: Move preempt_enable_no_resched() to the RT block
      mm: Disable NUMA_BALANCING_DEFAULT_ENABLED and TRANSPARENT_HUGEPAGE on PREEMPT_RT
      fscache: Use only one fscache_object_cong_wait.
      fscache: Use only one fscache_object_cong_wait.
      locking: Drop might_resched() from might_sleep_no_state_check()

Steven Rostedt (VMware) (1):
      Linux 5.10.78-rt56-rc1

----
 fs/fscache/internal.h   |  1 -
 fs/fscache/main.c       |  6 ------
 fs/fscache/object.c     | 13 +++++--------
 include/linux/kernel.h  |  2 +-
 include/linux/preempt.h |  6 +++---
 init/Kconfig            |  2 +-
 kernel/sched/core.c     |  2 +-
 kernel/sched/sched.h    |  3 +++
 localversion-rt         |  2 +-
 mm/zsmalloc.c           | 12 ++++++------
 10 files changed, 21 insertions(+), 28 deletions(-)

[PATCH RT 1/9] mm, zsmalloc: Convert zsmalloc_handle.lock to spinlock_t

[Steven Rostedt]

5.10.78-rt56-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Mike Galbraith <efault@gmx.de>

local_lock_t becoming a synonym of spinlock_t had consequences for the RT
mods to zsmalloc, which were taking a mutex while holding a local_lock,
inspiring a lockdep "BUG: Invalid wait context" gripe.

Converting zsmalloc_handle.lock to a spinlock_t restored lockdep silence.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 mm/zsmalloc.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 277d426c881f..3595c1644135 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -82,7 +82,7 @@
 
 struct zsmalloc_handle {
 	unsigned long addr;
-	struct mutex lock;
+	spinlock_t lock;
 };
 
 #define ZS_HANDLE_ALLOC_SIZE (sizeof(struct zsmalloc_handle))
@@ -370,7 +370,7 @@ static unsigned long cache_alloc_handle(struct zs_pool *pool, gfp_t gfp)
 	if (p) {
 		struct zsmalloc_handle *zh = p;
 
-		mutex_init(&zh->lock);
+		spin_lock_init(&zh->lock);
 	}
 #endif
 	return (unsigned long)p;
@@ -930,7 +930,7 @@ static inline int testpin_tag(unsigned long handle)
 #ifdef CONFIG_PREEMPT_RT
 	struct zsmalloc_handle *zh = zs_get_pure_handle(handle);
 
-	return mutex_is_locked(&zh->lock);
+	return spin_is_locked(&zh->lock);
 #else
 	return bit_spin_is_locked(HANDLE_PIN_BIT, (unsigned long *)handle);
 #endif
@@ -941,7 +941,7 @@ static inline int trypin_tag(unsigned long handle)
 #ifdef CONFIG_PREEMPT_RT
 	struct zsmalloc_handle *zh = zs_get_pure_handle(handle);
 
-	return mutex_trylock(&zh->lock);
+	return spin_trylock(&zh->lock);
 #else
 	return bit_spin_trylock(HANDLE_PIN_BIT, (unsigned long *)handle);
 #endif
@@ -952,7 +952,7 @@ static void pin_tag(unsigned long handle) __acquires(bitlock)
 #ifdef CONFIG_PREEMPT_RT
 	struct zsmalloc_handle *zh = zs_get_pure_handle(handle);
 
-	return mutex_lock(&zh->lock);
+	return spin_lock(&zh->lock);
 #else
 	bit_spin_lock(HANDLE_PIN_BIT, (unsigned long *)handle);
 #endif
@@ -963,7 +963,7 @@ static void unpin_tag(unsigned long handle) __releases(bitlock)
 #ifdef CONFIG_PREEMPT_RT
 	struct zsmalloc_handle *zh = zs_get_pure_handle(handle);
 
-	return mutex_unlock(&zh->lock);
+	return spin_unlock(&zh->lock);
 #else
 	bit_spin_unlock(HANDLE_PIN_BIT, (unsigned long *)handle);
 #endif
-- 
2.33.0

[PATCH RT 2/9] sched: Fix get_push_task() vs migrate_disable()

[Steven Rostedt]

5.10.78-rt56-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

push_rt_task() attempts to move the currently running task away if the
next runnable task has migration disabled and therefore is pinned on the
current CPU.

The current task is retrieved via get_push_task() which only checks for
nr_cpus_allowed == 1, but does not check whether the task has migration
disabled and therefore cannot be moved either. The consequence is a
pointless invocation of the migration thread which correctly observes
that the task cannot be moved.

Return NULL if the task has migration disabled and cannot be moved to
another CPU.

Cc: stable-rt@vger.kernel.org
Fixes: a7c81556ec4d3 ("sched: Fix migrate_disable() vs rt/dl balancing")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210826133738.yiotqbtdaxzjsnfj@linutronix.de
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/sched/sched.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 826ea17e144d..c2c9c386456d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1949,6 +1949,9 @@ static inline struct task_struct *get_push_task(struct rq *rq)
 	if (p->nr_cpus_allowed == 1)
 		return NULL;
 
+	if (p->migration_disabled)
+		return NULL;
+
 	rq->push_busy = true;
 	return get_task_struct(p);
 }
-- 
2.33.0

[PATCH RT 3/9] sched: Switch wait_task_inactive to HRTIMER_MODE_REL_HARD

[Steven Rostedt]

5.10.78-rt56-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

With PREEMPT_RT enabled all hrtimers callbacks will be invoked in
softirq mode unless they are explicitly marked as HRTIMER_MODE_HARD.
During boot kthread_bind() is used for the creation of per-CPU threads
and then hangs in wait_task_inactive() if the ksoftirqd is not
yet up and running.
The hang disappeared since commit
   26c7295be0c5e ("kthread: Do not preempt current task if it is going to call schedule()")

but enabling function trace on boot reliably leads to the freeze on boot
behaviour again.
The timer in wait_task_inactive() can not be directly used by an user
interface to abuse it and create a mass wake of several tasks at the
same time which would to long sections with disabled interrupts.
Therefore it is safe to make the timer HRTIMER_MODE_REL_HARD.

Switch the timer to HRTIMER_MODE_REL_HARD.

Cc: stable-rt@vger.kernel.org
Link: https://lkml.kernel.org/r/20210826170408.vm7rlj7odslshwch@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f638d9420553..54fa3bb1b7c4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2734,7 +2734,7 @@ unsigned long wait_task_inactive(struct task_struct *p, long match_state)
 			ktime_t to = NSEC_PER_SEC / HZ;
 
 			set_current_state(TASK_UNINTERRUPTIBLE);
-			schedule_hrtimeout(&to, HRTIMER_MODE_REL);
+			schedule_hrtimeout(&to, HRTIMER_MODE_REL_HARD);
 			continue;
 		}
 
-- 
2.33.0

[PATCH RT 4/9] preempt: Move preempt_enable_no_resched() to the RT block

[Steven Rostedt]

5.10.78-rt56-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

preempt_enable_no_resched() should point to preempt_enable() on
PREEMPT_RT so nobody is playing any preempt tricks and enables
preemption without checking for the need-resched flag.

This was misplaced in v3.14.0-rt1 und remained unnoticed until now.

Point preempt_enable_no_resched() and preempt_enable() on RT.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/preempt.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index af39859f02ee..7b5b2ed55531 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -208,12 +208,12 @@ do { \
 	preempt_count_dec(); \
 } while (0)
 
-#ifdef CONFIG_PREEMPT_RT
+#ifndef CONFIG_PREEMPT_RT
 # define preempt_enable_no_resched() sched_preempt_enable_no_resched()
-# define preempt_check_resched_rt() preempt_check_resched()
+# define preempt_check_resched_rt() barrier();
 #else
 # define preempt_enable_no_resched() preempt_enable()
-# define preempt_check_resched_rt() barrier();
+# define preempt_check_resched_rt() preempt_check_resched()
 #endif
 
 #define preemptible()	(preempt_count() == 0 && !irqs_disabled())
-- 
2.33.0

[PATCH RT 5/9] mm: Disable NUMA_BALANCING_DEFAULT_ENABLED and TRANSPARENT_HUGEPAGE on PREEMPT_RT

[Steven Rostedt]

5.10.78-rt56-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

TRANSPARENT_HUGEPAGE:
There are potential non-deterministic delays to an RT thread if a critical
memory region is not THP-aligned and a non-RT buffer is located in the same
hugepage-aligned region. It's also possible for an unrelated thread to migrate
pages belonging to an RT task incurring unexpected page faults due to memory
defragmentation even if khugepaged is disabled.

Regular HUGEPAGEs are not affected by this can be used.

NUMA_BALANCING:
There is a non-deterministic delay to mark PTEs PROT_NONE to gather NUMA fault
samples, increased page faults of regions even if mlocked and non-deterministic
delays when migrating pages.

[Mel Gorman worded 99% of the commit description].

Link: https://lore.kernel.org/all/20200304091159.GN3818@techsingularity.net/
Link: https://lore.kernel.org/all/20211026165100.ahz5bkx44lrrw5pt@linutronix.de/
Cc: stable-rt@vger.kernel.org
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lore.kernel.org/r/20211028143327.hfbxjze7palrpfgp@linutronix.de
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 init/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index 7ba2b602b707..9bfc60e7eead 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -861,7 +861,7 @@ config NUMA_BALANCING
 	bool "Memory placement aware NUMA scheduler"
 	depends on ARCH_SUPPORTS_NUMA_BALANCING
 	depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
-	depends on SMP && NUMA && MIGRATION
+	depends on SMP && NUMA && MIGRATION && !PREEMPT_RT
 	help
 	  This option adds support for automatic NUMA aware memory/task placement.
 	  The mechanism is quite primitive and is based on migrating memory when
-- 
2.33.0

[PATCH RT 6/9] fscache: Use only one fscache_object_cong_wait.

[Steven Rostedt]

5.10.78-rt56-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

In the commit mentioned below, fscache was converted from slow-work to
workqueue. slow_work_enqueue() and slow_work_sleep_till_thread_needed()
did not use a per-CPU workqueue. They choose from two global waitqueues
depending on the SLOW_WORK_VERY_SLOW bit which was not set so it always
one waitqueue.

I can't find out how it is ensured that a waiter on certain CPU is woken
up be the other side. My guess is that the timeout in schedule_timeout()
ensures that it does not wait forever (or a random wake up).

fscache_object_sleep_till_congested() must be invoked from preemptible
context in order for schedule() to work. In this case this_cpu_ptr()
should complain with CONFIG_DEBUG_PREEMPT enabled except the thread is
bound to one CPU.

wake_up() wakes only one waiter and I'm not sure if it is guaranteed
that only one waiter exists.

Replace the per-CPU waitqueue with one global waitqueue.

Fixes: 8b8edefa2fffb ("fscache: convert object to use workqueue instead of slow-work")
Reported-by: Gregor Beck <gregor.beck@gmail.com>
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 fs/fscache/internal.h |  1 -
 fs/fscache/main.c     |  6 ------
 fs/fscache/object.c   | 11 +++++------
 3 files changed, 5 insertions(+), 13 deletions(-)

diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index 64aa552b296d..7dae569dafb9 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -95,7 +95,6 @@ extern unsigned fscache_debug;
 extern struct kobject *fscache_root;
 extern struct workqueue_struct *fscache_object_wq;
 extern struct workqueue_struct *fscache_op_wq;
-DECLARE_PER_CPU(wait_queue_head_t, fscache_object_cong_wait);
 
 extern unsigned int fscache_hash(unsigned int salt, unsigned int *data, unsigned int n);
 
diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index 4207f98e405f..85f8cf3a323d 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -41,8 +41,6 @@ struct kobject *fscache_root;
 struct workqueue_struct *fscache_object_wq;
 struct workqueue_struct *fscache_op_wq;
 
-DEFINE_PER_CPU(wait_queue_head_t, fscache_object_cong_wait);
-
 /* these values serve as lower bounds, will be adjusted in fscache_init() */
 static unsigned fscache_object_max_active = 4;
 static unsigned fscache_op_max_active = 2;
@@ -138,7 +136,6 @@ unsigned int fscache_hash(unsigned int salt, unsigned int *data, unsigned int n)
 static int __init fscache_init(void)
 {
 	unsigned int nr_cpus = num_possible_cpus();
-	unsigned int cpu;
 	int ret;
 
 	fscache_object_max_active =
@@ -161,9 +158,6 @@ static int __init fscache_init(void)
 	if (!fscache_op_wq)
 		goto error_op_wq;
 
-	for_each_possible_cpu(cpu)
-		init_waitqueue_head(&per_cpu(fscache_object_cong_wait, cpu));
-
 	ret = fscache_proc_init();
 	if (ret < 0)
 		goto error_proc;
diff --git a/fs/fscache/object.c b/fs/fscache/object.c
index cb2146e02cd5..55158f30d093 100644
--- a/fs/fscache/object.c
+++ b/fs/fscache/object.c
@@ -807,6 +807,8 @@ void fscache_object_destroy(struct fscache_object *object)
 }
 EXPORT_SYMBOL(fscache_object_destroy);
 
+static DECLARE_WAIT_QUEUE_HEAD(fscache_object_cong_wait);
+
 /*
  * enqueue an object for metadata-type processing
  */
@@ -815,12 +817,10 @@ void fscache_enqueue_object(struct fscache_object *object)
 	_enter("{OBJ%x}", object->debug_id);
 
 	if (fscache_get_object(object, fscache_obj_get_queue) >= 0) {
-		wait_queue_head_t *cong_wq =
-			&get_cpu_var(fscache_object_cong_wait);
 
 		if (queue_work(fscache_object_wq, &object->work)) {
 			if (fscache_object_congested())
-				wake_up(cong_wq);
+				wake_up(&fscache_object_cong_wait);
 		} else
 			fscache_put_object(object, fscache_obj_put_queue);
 
@@ -842,16 +842,15 @@ void fscache_enqueue_object(struct fscache_object *object)
  */
 bool fscache_object_sleep_till_congested(signed long *timeoutp)
 {
-	wait_queue_head_t *cong_wq = this_cpu_ptr(&fscache_object_cong_wait);
 	DEFINE_WAIT(wait);
 
 	if (fscache_object_congested())
 		return true;
 
-	add_wait_queue_exclusive(cong_wq, &wait);
+	add_wait_queue_exclusive(&fscache_object_cong_wait, &wait);
 	if (!fscache_object_congested())
 		*timeoutp = schedule_timeout(*timeoutp);
-	finish_wait(cong_wq, &wait);
+	finish_wait(&fscache_object_cong_wait, &wait);
 
 	return fscache_object_congested();
 }
-- 
2.33.0

[PATCH RT 7/9] fscache: Use only one fscache_object_cong_wait. [update]

[Steven Rostedt]

5.10.78-rt56-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

This is an update of the original patch, removing put_cpu_var() which
was overseen in the initial patch.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 fs/fscache/object.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/fs/fscache/object.c b/fs/fscache/object.c
index 55158f30d093..fb9794dce721 100644
--- a/fs/fscache/object.c
+++ b/fs/fscache/object.c
@@ -823,8 +823,6 @@ void fscache_enqueue_object(struct fscache_object *object)
 				wake_up(&fscache_object_cong_wait);
 		} else
 			fscache_put_object(object, fscache_obj_put_queue);
-
-		put_cpu_var(fscache_object_cong_wait);
 	}
 }
 
-- 
2.33.0

[PATCH RT 8/9] locking: Drop might_resched() from might_sleep_no_state_check()

[Steven Rostedt]

5.10.78-rt56-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

might_sleep_no_state_check() serves the same purpose as might_sleep()
except it is used before sleeping locks are acquired and therefore does
not check task_struct::state because the state is preserved.

That state is preserved in the locking slow path so we must not schedule
at the begin of the locking function because the state will be lost and
not preserved at that time.

Remove might_resched() from might_sleep_no_state_check() to avoid losing the
state before it is preserved.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/kernel.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 2cff7554395d..6eb0ab994f4c 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -222,7 +222,7 @@ extern void __cant_migrate(const char *file, int line);
 	do { __might_sleep(__FILE__, __LINE__, 0); might_resched(); } while (0)
 
 # define might_sleep_no_state_check() \
-	do { ___might_sleep(__FILE__, __LINE__, 0); might_resched(); } while (0)
+	do { ___might_sleep(__FILE__, __LINE__, 0); } while (0)
 
 /**
  * cant_sleep - annotation for functions that cannot sleep
-- 
2.33.0

[PATCH RT 9/9] Linux 5.10.78-rt56-rc1

[Steven Rostedt]

5.10.78-rt56-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

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

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

diff --git a/localversion-rt b/localversion-rt
index 51b05e9abe6f..a6adf38a57d4 100644
--- a/localversion-rt
+++ b/localversion-rt
@@ -1 +1 @@
--rt55
+-rt56-rc1
-- 
2.33.0