Hi Paul,
On Tue, 25 Mar 2025 at 15:36, Paul E. McKenney <paulmck@xxxxxxxxxx> 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@xxxxxxxxx> wrote:
> > > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxx>
> > > Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> >
> > 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_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?
>
> ... 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@xxxxxxxxxx>
> 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@xxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/CAMuHMdX6dy9_tmpLkpcnGzxyRbe6qSWYukcPp=H1GzZdyd3qBQ@xxxxxxxxxxxxxx/
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxx
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
