[ANNOUNCE] v5.4.28-rt19v5.4.28-rt19-patches

Dear RT folks!

I'm pleased to announce the v5.4.28-rt19 patch set.

Changes since v5.4.28-rt18:

  - Memory compaction of unevictable pages has been disabled in the v5.4
    release. This aligns the change with what has been prepared for
    upstream: Disable is by default on PREEMPT_RT
    (/proc/sys/vm/compact_unevictable_allowed reads 0) but allow
    enabling it which will trigger a warning.

Known issues
     - It has been pointed out that due to changes to the printk code the
       internal buffer representation changed. This is only an issue if tools
       like `crash' are used to extract the printk buffer from a kernel memory
       image.

The delta patch against v5.4.28-rt18 is appended below and can be found here:

     https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.4/incr/patch-5.4.28-rt18-rt19.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 v5.4.28-rt19

The RT patch against v5.4.28 can be found here:

    https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patch-5.4.28-rt19.patch.xz

The split quilt queue is available at:

    https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.28-rt19.tar.xz

Sebastian

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

4 files changed, 104 insertions, 22 deletions

diff --git a/patches/localversion.patch b/patches/localversion.patch
index 48a458c6f3b7..19d7ea05016c 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 @@
-+-rt18
++-rt19
diff --git a/patches/mm-compaction-Disable-compact_unevictable_allowed-on.patch b/patches/mm-compaction-Disable-compact_unevictable_allowed-on.patch
index 4d0605cf5345..8381662480c4 100644
--- a/patches/mm-compaction-Disable-compact_unevictable_allowed-on.patch
+++ b/patches/mm-compaction-Disable-compact_unevictable_allowed-on.patch
@@ -9,35 +9,83 @@ it is allowed to examine mlocked pages and compact them by default.
 On -RT even minor pagefaults are problematic because it may take a few
 100us to resolve them and until then the task is blocked.
 
-Make compact_unevictable_allowed = 0 default and remove it from /proc on
-RT.
+Make compact_unevictable_allowed = 0 default and issue a warning on RT
+if it is changed.
 
 Link: https://lore.kernel.org/linux-mm/20190710144138.qyn4tuttdq6h7kqx@linutronix.de/
+Acked-by: Mel Gorman <mgorman@techsingularity.net>
+Acked-by: Vlastimil Babka <vbabka@suse.cz>
 Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
 ---
- kernel/sysctl.c |    3 ++-
- mm/compaction.c |    4 ++++
- 2 files changed, 6 insertions(+), 1 deletion(-)
+ Documentation/admin-guide/sysctl/vm.rst |    3 +++
+ kernel/sysctl.c                         |   29 ++++++++++++++++++++++++++++-
+ mm/compaction.c                         |    4 ++++
+ 3 files changed, 35 insertions(+), 1 deletion(-)
 
+--- a/Documentation/admin-guide/sysctl/vm.rst
++++ b/Documentation/admin-guide/sysctl/vm.rst
+@@ -128,6 +128,9 @@ allowed to examine the unevictable lru (
+ This should be used on systems where stalls for minor page faults are an
+ acceptable trade for large contiguous free memory.  Set to 0 to prevent
+ compaction from moving pages that are unevictable.  Default value is 1.
++On CONFIG_PREEMPT_RT the default value is 0 in order to avoid a page fault, due
++to compaction, which would block the task from becomming active until the fault
++is resolved.
+ 
+ 
+ dirty_background_bytes
 --- a/kernel/sysctl.c
 +++ b/kernel/sysctl.c
-@@ -1488,6 +1488,7 @@ static struct ctl_table vm_table[] = {
- 		.extra1		= &min_extfrag_threshold,
- 		.extra2		= &max_extfrag_threshold,
- 	},
-+#ifndef CONFIG_PREEMPT_RT
- 	{
- 		.procname	= "compact_unevictable_allowed",
+@@ -212,6 +212,11 @@ static int proc_do_cad_pid(struct ctl_ta
+ 		  void __user *buffer, size_t *lenp, loff_t *ppos);
+ static int proc_taint(struct ctl_table *table, int write,
+ 			       void __user *buffer, size_t *lenp, loff_t *ppos);
++#ifdef CONFIG_COMPACTION
++static int proc_dointvec_minmax_warn_RT_change(struct ctl_table *table,
++					       int write, void __user *buffer,
++					       size_t *lenp, loff_t *ppos);
++#endif
+ #endif
+ 
+ #ifdef CONFIG_PRINTK
+@@ -1493,7 +1498,7 @@ static struct ctl_table vm_table[] = {
  		.data		= &sysctl_compact_unevictable_allowed,
-@@ -1497,7 +1498,7 @@ static struct ctl_table vm_table[] = {
+ 		.maxlen		= sizeof(int),
+ 		.mode		= 0644,
+-		.proc_handler	= proc_dointvec_minmax,
++		.proc_handler	= proc_dointvec_minmax_warn_RT_change,
  		.extra1		= SYSCTL_ZERO,
  		.extra2		= SYSCTL_ONE,
  	},
--
+@@ -2581,6 +2586,28 @@ int proc_dointvec(struct ctl_table *tabl
+ 	return do_proc_dointvec(table, write, buffer, lenp, ppos, NULL, NULL);
+ }
+ 
++#ifdef CONFIG_COMPACTION
++static int proc_dointvec_minmax_warn_RT_change(struct ctl_table *table,
++					       int write, void __user *buffer,
++					       size_t *lenp, loff_t *ppos)
++{
++	int ret, old;
++
++	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || !write)
++		return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
++
++	old = *(int *)table->data;
++	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
++	if (ret)
++		return ret;
++	if (old != *(int *)table->data)
++		pr_warn_once("sysctl attribute %s changed by %s[%d]\n",
++			     table->procname, current->comm,
++			     task_pid_nr(current));
++	return ret;
++}
 +#endif
- #endif /* CONFIG_COMPACTION */
- 	{
- 		.procname	= "min_free_kbytes",
++
+ /**
+  * proc_douintvec - read a vector of unsigned integers
+  * @table: the sysctl table
 --- a/mm/compaction.c
 +++ b/mm/compaction.c
 @@ -1590,7 +1590,11 @@ typedef enum {
@@ -45,7 +93,7 @@ Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
   * compactable pages.
   */
 +#ifdef CONFIG_PREEMPT_RT
-+#define sysctl_compact_unevictable_allowed 0
++int sysctl_compact_unevictable_allowed __read_mostly = 0;
 +#else
  int sysctl_compact_unevictable_allowed __read_mostly = 1;
 +#endif
diff --git a/patches/mm-compaction-Really-limit-compact_unevictable_allow.patch b/patches/mm-compaction-Really-limit-compact_unevictable_allow.patch
new file mode 100644
index 000000000000..b34687eac03b
--- /dev/null
+++ b/patches/mm-compaction-Really-limit-compact_unevictable_allow.patch
@@ -0,0 +1,32 @@
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Date: Tue, 3 Mar 2020 13:43:25 +0100
+Subject: [PATCH] =?UTF-8?q?mm/compaction:=20Really=20limit=20compact=5Fune?=
+ =?UTF-8?q?victable=5Fallowed=20to=200=E2=80=A61?=
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+The proc file `compact_unevictable_allowed' should allow 0 and 1 only,
+the `extra*' attribues have been set properly but without
+proc_dointvec_minmax() as the `proc_handler' the limit will not be
+enforced.
+
+Use proc_dointvec_minmax() as the `proc_handler' to enfoce the valid
+specified range.
+
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ kernel/sysctl.c |    2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/kernel/sysctl.c
++++ b/kernel/sysctl.c
+@@ -1493,7 +1493,7 @@ static struct ctl_table vm_table[] = {
+ 		.data		= &sysctl_compact_unevictable_allowed,
+ 		.maxlen		= sizeof(int),
+ 		.mode		= 0644,
+-		.proc_handler	= proc_dointvec,
++		.proc_handler	= proc_dointvec_minmax,
+ 		.extra1		= SYSCTL_ZERO,
+ 		.extra2		= SYSCTL_ONE,
+ 	},
diff --git a/patches/series b/patches/series
index 07da648a4c55..7da82726cfe9 100644
--- a/patches/series
+++ b/patches/series
@@ -124,6 +124,11 @@ smp-Remove-allocation-mask-from-on_each_cpu_cond.patch
 # 20200224140726.1550689-1-bigeasy@linutronix.de
 drm-vmwgfx-Drop-preempt_disable-in-vmw_fifo_ping_hos.patch
 
+# 20200303202054.gsosv7fsx2ma3cic@linutronix.de
+mm-compaction-Really-limit-compact_unevictable_allow.patch
+# 20200319165536.ovi75tsr2seared4@linutronix.de
+mm-compaction-Disable-compact_unevictable_allowed-on.patch
+
 ############################################################
 # Ready for posting
 ############################################################
@@ -137,9 +142,6 @@ Use-CONFIG_PREEMPTION.patch
 0003-workqueue-Use-swait-for-wq_manager_wait.patch
 0004-workqueue-Convert-the-locks-to-raw-type.patch
 
-# XXX
-mm-compaction-Disable-compact_unevictable_allowed-on.patch
-
 ############################################################
 # Needs to address review feedback
 ############################################################