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authorThomas Gleixner <tglx@linutronix.de>2020-02-08 20:48:29 +0100
committerThomas Gleixner <tglx@linutronix.de>2020-02-20 21:17:24 +0100
commit66630058e56b26b3a9cf2625e250a8c592dd0207 (patch)
tree871b982917fc109f20c220b58f477dd138ce66f2 /include/linux/preempt.h
parent11a48a5a18c63fd7621bb050228cebf13566e4d8 (diff)
sched/rt: Provide migrate_disable/enable() inlines
Code which solely needs to prevent migration of a task uses preempt_disable()/enable() pairs. This is the only reliable way to do so as setting the task affinity to a single CPU can be undone by a setaffinity operation from a different task/process. RT provides a seperate migrate_disable/enable() mechanism which does not disable preemption to achieve the semantic requirements of a (almost) fully preemptible kernel. As it is unclear from looking at a given code path whether the intention is to disable preemption or migration, introduce migrate_disable/enable() inline functions which can be used to annotate code which merely needs to disable migration. Map them to preempt_disable/enable() for now. The RT substitution will be provided later. Code which is annotated that way documents that it has no requirement to protect against reentrancy of a preempting task. Either this is not required at all or the call sites are already serialized by other means. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ben Segall <bsegall@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Link: https://lore.kernel.org/r/878slclv1u.fsf@nanos.tec.linutronix.de
Diffstat (limited to 'include/linux/preempt.h')
-rw-r--r--include/linux/preempt.h30
1 files changed, 30 insertions, 0 deletions
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index bbb68dba37cc..bc3f1aecaa19 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -322,4 +322,34 @@ static inline void preempt_notifier_init(struct preempt_notifier *notifier,
#endif
+/**
+ * migrate_disable - Prevent migration of the current task
+ *
+ * Maps to preempt_disable() which also disables preemption. Use
+ * migrate_disable() to annotate that the intent is to prevent migration,
+ * but not necessarily preemption.
+ *
+ * Can be invoked nested like preempt_disable() and needs the corresponding
+ * number of migrate_enable() invocations.
+ */
+static __always_inline void migrate_disable(void)
+{
+ preempt_disable();
+}
+
+/**
+ * migrate_enable - Allow migration of the current task
+ *
+ * Counterpart to migrate_disable().
+ *
+ * As migrate_disable() can be invoked nested, only the outermost invocation
+ * reenables migration.
+ *
+ * Currently mapped to preempt_enable().
+ */
+static __always_inline void migrate_enable(void)
+{
+ preempt_enable();
+}
+
#endif /* __LINUX_PREEMPT_H */