Augment rt_task() with is_realtime()

Whenever the kernel checks for rt_task() to avoid delaying real-time
tasks, we want it to also not delay LITMUS^RT tasks.  Hence, most
calls to rt_task() should be matched by an equivalent call to
is_realtime().

Notably, this affects the implementations of select() and nanosleep(),
which use timer_slack_ns when setting up timers for non-real-time
tasks.

5 files changed, 17 insertions, 6 deletions

diff --git a/fs/select.c b/fs/select.c
index 8c1c96c27062..f53b3e421c26 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -28,6 +28,8 @@
 #include <linux/hrtimer.h>
 #include <linux/sched/rt.h>
 
+#include <litmus/litmus.h> /* for is_realtime() */
+
 #include <asm/uaccess.h>
 
 
@@ -77,7 +79,7 @@ long select_estimate_accuracy(struct timespec *tv)
          * Realtime tasks get a slack of 0 for obvious reasons.
          */
 
-        if (rt_task(current))
+        if (rt_task(current) || is_realtime(current))
                 return 0;
 
         ktime_get_ts(&now);
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index c7f0c79b2cb5..60b6329ab222 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -49,6 +49,7 @@
 #include <linux/timer.h>
 
 #include <litmus/debug_trace.h>
+#include <litmus/litmus.h>
 
 #include <asm/uaccess.h>
 
@@ -1701,7 +1702,7 @@ long hrtimer_nanosleep(struct timespec *rqtp, struct timespec __user *rmtp,
         unsigned long slack;
 
         slack = current->timer_slack_ns;
-        if (rt_task(current))
+        if (rt_task(current) || is_realtime(current))
                 slack = 0;
 
         hrtimer_init_on_stack(&t.timer, clockid, mode);
diff --git a/kernel/mutex.c b/kernel/mutex.c
index ad53a664f113..a60d05e9498f 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -25,6 +25,8 @@
 #include <linux/interrupt.h>
 #include <linux/debug_locks.h>
 
+#include <litmus/litmus.h>
+
 /*
  * In the DEBUG case we are using the "NULL fastpath" for mutexes,
  * which forces all calls into the slowpath:
@@ -325,7 +327,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                  * we're an RT task that will live-lock because we won't let
                  * the owner complete.
                  */
-                if (!owner && (need_resched() || rt_task(task)))
+                if (!owner && (need_resched() ||
+                               rt_task(task) || is_realtime(task)))
                         break;
 
                 /*
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 4514ad7415c3..03ce78694ed9 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -38,6 +38,8 @@
 #include <linux/sched/rt.h>
 #include <trace/events/writeback.h>
 
+#include <litmus/litmus.h> /* for is_realtime() */
+
 /*
  * Sleep at most 200ms at a time in balance_dirty_pages().
  */
@@ -279,7 +281,7 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
         if (background >= dirty)
                 background = dirty / 2;
         tsk = current;
-        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
+        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk) || is_realtime(tsk)) {
                 background += background / 4;
                 dirty += dirty / 4;
         }
@@ -333,7 +335,7 @@ static unsigned long zone_dirty_limit(struct zone *zone)
         else
                 dirty = vm_dirty_ratio * zone_memory / 100;
 
-        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
+        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk) || is_realtime(tsk))
                 dirty += dirty / 4;
 
         return dirty;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2ee0fd313f03..65299391e760 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -61,6 +61,8 @@
 #include <linux/hugetlb.h>
 #include <linux/sched/rt.h>
 
+#include <litmus/litmus.h> /* for is_realtime() */
+
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
 #include "internal.h"
@@ -2362,7 +2364,8 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
                  * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
                  */
                 alloc_flags &= ~ALLOC_CPUSET;
-        } else if (unlikely(rt_task(current)) && !in_interrupt())
+        } else if (unlikely(rt_task(current) || is_realtime(current))
+                   && !in_interrupt())
                 alloc_flags |= ALLOC_HARDER;
 
         if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) {