[tip: sched/rt] sched: Provide cant_migrate()

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the sched/rt branch of tip:

Commit-ID:     4e139c7711633365ebb52fbb63905395522a8413
Gitweb:        https://git.kernel.org/tip/4e139c7711633365ebb52fbb63905395522a8413
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Fri, 14 Feb 2020 14:39:19 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Thu, 20 Feb 2020 21:17:24 +01:00

sched: Provide cant_migrate()

Some code pathes rely on preempt_disable() to prevent migration on a non RT
enabled kernel. These preempt_disable/enable() pairs are substituted by
migrate_disable/enable() pairs or other forms of RT specific protection. On
RT these protections prevent migration but not preemption. Obviously a
cant_sleep() check in such a section will trigger on RT because preemption
is not disabled.

Provide a cant_migrate() macro which maps to cant_sleep() on a non RT
kernel and an empty placeholder for RT for now. The placeholder will be
changed to a proper debug check along with the RT specific migration
protection mechanism.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200214161503.070487511@xxxxxxxxxxxxx
---
 include/linux/kernel.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 0d9db2a..9b7a8d7 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -257,6 +257,13 @@ extern void __cant_sleep(const char *file, int line, int preempt_offset);
 
 #define might_sleep_if(cond) do { if (cond) might_sleep(); } while (0)
 
+#ifndef CONFIG_PREEMPT_RT
+# define cant_migrate()		cant_sleep()
+#else
+  /* Placeholder for now */
+# define cant_migrate()		do { } while (0)
+#endif
+
 /**
  * abs - return absolute value of an argument
  * @x: the value.  If it is unsigned type, it is converted to signed type first.