rcu: Provide RCU CPU stall warnings for tiny RCU

Tiny RCU has historically omitted RCU CPU stall warnings in order to
reduce memory requirements, however, lack of these warnings caused
Thomas Gleixner some debugging pain recently.  Therefore, this commit
adds RCU CPU stall warnings to tiny RCU if RCU_TRACE=y.  This keeps
the memory footprint small, while still enabling CPU stall warnings
in kernels built to enable them.

Updated to include Josh Triplett's suggested use of RCU_STALL_COMMON
config variable to simplify #if expressions.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 7d30240e5bfe..a5e90e139ba5 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -486,6 +486,14 @@ config PREEMPT_RCU
           This option enables preemptible-RCU code that is common between
           the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
 
+config RCU_STALL_COMMON
+        def_bool ( TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE )
+        help
+          This option enables RCU CPU stall code that is common between
+          the TINY and TREE variants of RCU.  The purpose is to allow
+          the tiny variants to disable RCU CPU stall warnings, while
+          making these warnings mandatory for the tree variants.
+
 config CONTEXT_TRACKING
        bool