On Tue, Mar 25, 2025 at 03:57:43PM +0100, Geert Uytterhoeven wrote:
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?
The FORCE_NEED_SRCU_NMI_SAFE has no effect otherwise, so it cannot hurt. Again, please see below.
Thanx, Paul
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
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commit 2245ef8605a80726548253d885b4cadd97f69f3b 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. Given that this new FORCE_NEED_SRCU_NMI_SAFE Kconfig option has no effect unless the ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option is also selected, it also depends on this Kconfig option.
[ paulmck: Apply Geert Uytterhoeven feedback. ]
Reported-by: Geert Uytterhoeven geert@linux-m68k.org Closes: https://lore.kernel.org/all/CAMuHMdX6dy9_tmpLkpcnGzxyRbe6qSWYukcPp=H1GzZdyd3... Signed-off-by: Paul E. McKenney paulmck@kernel.org
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index b3f985d41717a..ceaf6594f634c 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -68,6 +68,8 @@ 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 + depends on ARCH_HAS_NMI_SAFE_THIS_CPU_OPS select NEED_SRCU_NMI_SAFE default n help