preempt/dynamic: Provide cond_resched() and might_resched() static calls

Provide static calls to control cond_resched() (called in !CONFIG_PREEMPT)
and might_resched() (called in CONFIG_PREEMPT_VOLUNTARY) to that we
can override their behaviour when preempt= is overriden.

Since the default behaviour is full preemption, both their calls are
ignored when preempt= isn't passed.

  [fweisbec: branch might_resched() directly to __cond_resched(), only
             define static calls when PREEMPT_DYNAMIC]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210118141223.123667-6-frederic@kernel.org

1 files changed, 19 insertions, 4 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index f7902d8c1048..cfd3d349f905 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -15,7 +15,7 @@
 #include <linux/typecheck.h>
 #include <linux/printk.h>
 #include <linux/build_bug.h>
-
+#include <linux/static_call_types.h>
 #include <asm/byteorder.h>
 
 #include <uapi/linux/kernel.h>
@@ -81,11 +81,26 @@ struct pt_regs;
 struct user;
 
 #ifdef CONFIG_PREEMPT_VOLUNTARY
-extern int _cond_resched(void);
-# define might_resched() _cond_resched()
+
+extern int __cond_resched(void);
+# define might_resched() __cond_resched()
+
+#elif defined(CONFIG_PREEMPT_DYNAMIC)
+
+extern int __cond_resched(void);
+
+DECLARE_STATIC_CALL(might_resched, __cond_resched);
+
+static __always_inline void might_resched(void)
+{
+	static_call(might_resched)();
+}
+
 #else
+
 # define might_resched() do { } while (0)
-#endif
+
+#endif /* CONFIG_PREEMPT_* */
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 extern void ___might_sleep(const char *file, int line, int preempt_offset);