Hi Paul,
On Tue, 25 Mar 2025 at 15:36, Paul E. McKenney paulmck@kernel.org wrote:
On Tue, Mar 25, 2025 at 09:04:31AM +0100, Geert Uytterhoeven wrote:
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?
Yes, you should select "n" unless ...
depends on !TINY_SRCUselect NEED_SRCU_NMI_SAFEdefault nhelpThis option forces selection of the NEED_SRCU_NMI_SAFEKconfig 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?
... you are on a system selecting ARCH_HAS_NMI_SAFE_THIS_CPU_OPS and
So a dependency on ARCH_HAS_NMI_SAFE_THIS_CPU_OPS does make sense, doesn't it?
you would like to test the SRCU setup that needed only by systems that do not select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS.
Ah. I forgot to add "depends on RCU_EXPERT".
Yes, that makes sense.
Apologies, I will fix this. Does the patch show below do the trick?
Thanx, Paul
commit b5c8c6f89c6d7ac778e961ad4b883eada0c1f42a Author: Paul E. McKenney paulmck@kernel.org Date: Tue Mar 25 07:31:45 2025 -0700
srcu: Make FORCE_NEED_SRCU_NMI_SAFE depend on RCU_EXPERT The FORCE_NEED_SRCU_NMI_SAFE is useful only for those wishing to test the SRCU code paths that accommodate architectures that do not have NMI-safe per-CPU operations, that is, those architectures that do not select the ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option. As such, this is a specialized Kconfig option that is not intended for casual users. This commit therefore hides it behind the RCU_EXPERT Kconfig option. Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> Closes: https://lore.kernel.org/all/CAMuHMdX6dy9_tmpLkpcnGzxyRbe6qSWYukcPp=H1GzZdyd3qBQ@mail.gmail.com/ Signed-off-by: Paul E. McKenney <paulmck@kernel.org>diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index b3f985d41717a..cc4ce79f58aa6 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -68,6 +68,7 @@ config TREE_SRCU config FORCE_NEED_SRCU_NMI_SAFE bool "Force selection of NEED_SRCU_NMI_SAFE" depends on !TINY_SRCU
depends on RCU_EXPERT select NEED_SRCU_NMI_SAFE default n help
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds