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authorThomas Gleixner <tglx@linutronix.de>2022-08-25 19:41:24 +0300
committerThomas Gleixner <tglx@linutronix.de>2022-09-19 15:35:07 +0300
commit555bb4ccd1dd78d0263eae31629fe1fdd65c1fb5 (patch)
tree88891b9221198fa70d63dc7be7cfa38aa1475318 /include/linux/preempt.h
parent521a547ced6477c54b4b0cc206000406c221b4d6 (diff)
downloadlinux-555bb4ccd1dd78d0263eae31629fe1fdd65c1fb5.tar.xz
preempt: Provide preempt_[dis|en]able_nested()
On PREEMPT_RT enabled kernels, spinlocks and rwlocks are neither disabling preemption nor interrupts. Though there are a few places which depend on the implicit preemption/interrupt disable of those locks, e.g. seqcount write sections, per CPU statistics updates etc. To avoid sprinkling CONFIG_PREEMPT_RT conditionals all over the place, add preempt_disable_nested() and preempt_enable_nested() which should be descriptive enough. Add a lockdep assertion for the !PREEMPT_RT case to catch callers which do not have preemption disabled. Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20220825164131.402717-2-bigeasy@linutronix.de
Diffstat (limited to 'include/linux/preempt.h')
-rw-r--r--include/linux/preempt.h42
1 files changed, 42 insertions, 0 deletions
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index b4381f255a5c..0df425bf9bd7 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -421,4 +421,46 @@ static inline void migrate_enable(void) { }
#endif /* CONFIG_SMP */
+/**
+ * preempt_disable_nested - Disable preemption inside a normally preempt disabled section
+ *
+ * Use for code which requires preemption protection inside a critical
+ * section which has preemption disabled implicitly on non-PREEMPT_RT
+ * enabled kernels, by e.g.:
+ * - holding a spinlock/rwlock
+ * - soft interrupt context
+ * - regular interrupt handlers
+ *
+ * On PREEMPT_RT enabled kernels spinlock/rwlock held sections, soft
+ * interrupt context and regular interrupt handlers are preemptible and
+ * only prevent migration. preempt_disable_nested() ensures that preemption
+ * is disabled for cases which require CPU local serialization even on
+ * PREEMPT_RT. For non-PREEMPT_RT kernels this is a NOP.
+ *
+ * The use cases are code sequences which are not serialized by a
+ * particular lock instance, e.g.:
+ * - seqcount write side critical sections where the seqcount is not
+ * associated to a particular lock and therefore the automatic
+ * protection mechanism does not work. This prevents a live lock
+ * against a preempting high priority reader.
+ * - RMW per CPU variable updates like vmstat.
+ */
+/* Macro to avoid header recursion hell vs. lockdep */
+#define preempt_disable_nested() \
+do { \
+ if (IS_ENABLED(CONFIG_PREEMPT_RT)) \
+ preempt_disable(); \
+ else \
+ lockdep_assert_preemption_disabled(); \
+} while (0)
+
+/**
+ * preempt_enable_nested - Undo the effect of preempt_disable_nested()
+ */
+static __always_inline void preempt_enable_nested(void)
+{
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_enable();
+}
+
#endif /* __LINUX_PREEMPT_H */