Re: [PATCH rcu 10/11] srcu: Add FORCE_NEED_SRCU_NMI_SAFE Kconfig for testing

Hi Boqun, Paul,

On Wed, 19 Feb 2025 at 16:44, Boqun Feng boqun.feng@gmail.com wrote:

From: "Paul E. McKenney" paulmck@kernel.org

The srcu_read_lock_nmisafe() and srcu_read_unlock_nmisafe() functions map to __srcu_read_lock() and __srcu_read_unlock() on systems like x86 that have NMI-safe this_cpu_inc() operations. This makes the underlying __srcu_read_lock_nmisafe() and __srcu_read_unlock_nmisafe() functions difficult to test on (for example) x86 systems, allowing bugs to creep in.

This commit therefore creates a FORCE_NEED_SRCU_NMI_SAFE Kconfig that forces those underlying functions to be used even on systems where they are not needed, thus providing better testing coverage.

Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Boqun Feng boqun.feng@gmail.com

Thanks for your patch, which is now commit 536e8b9b80bc7a0a ("srcu: Add FORCE_NEED_SRCU_NMI_SAFE Kconfig for testing") in linus/master

--- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -65,6 +65,17 @@ config TREE_SRCU help This option selects the full-fledged version of SRCU.

+config FORCE_NEED_SRCU_NMI_SAFE

•   bool "Force selection of NEED_SRCU_NMI_SAFE"
  

What am I supposed to answer here? "n" I guess. What about distro and allmodconfig kernels?

•   depends on !TINY_SRCU
  

•   select NEED_SRCU_NMI_SAFE
  

•   default n
  

•   help
  

•     This option forces selection of the NEED_SRCU_NMI_SAFE
  

•     Kconfig option, allowing testing of srcu_read_lock_nmisafe()
  

•     and srcu_read_unlock_nmisafe() on architectures (like x86)
  

•     that select the ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option.
  

Perhaps this should depend on ARCH_HAS_NMI_SAFE_THIS_CPU_OPS?

config NEED_SRCU_NMI_SAFE def_bool HAVE_NMI && !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS && !TINY_SRCU

Gr{oetje,eeting}s,

Geert