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    SubjectRe: [PATCH v2 rcu 0/8] NMI-safe SRCU reader API
    On Thu, Oct 20, 2022 at 12:05:37AM +0200, Frederic Weisbecker wrote:
    > On Wed, Oct 19, 2022 at 12:14:18PM -0700, Paul E. McKenney wrote:
    > > On Wed, Oct 19, 2022 at 01:19:53PM +0206, John Ogness wrote:
    > > > On 2022-10-18, "Paul E. McKenney" <paulmck@kernel.org> wrote:
    > > > > And the v6.1-rc1 stack is now at srcunmisafe.2022.10.18b.
    > > >
    > > > Thanks!
    > > >
    > > > I guess the kernel test robot will catch this, but if you checkout
    > > > commit 79c95dc428ad ("arch/x86: Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
    > > > Kconfig option") and build for x86_64, you will get:
    > > >
    > > > x86_64-linux-gnu-ld: kernel/rcu/srcutree.o: in function `srcu_gp_start_if_needed':
    > > > srcutree.c:(.text+0x133a): undefined reference to `__srcu_read_lock_nmisafe'
    > > > x86_64-linux-gnu-ld: srcutree.c:(.text+0x1490): undefined reference to `__srcu_read_unlock_nmisafe'
    > > > x86_64-linux-gnu-ld: kernel/rcu/srcutree.o: in function `srcu_barrier':
    > > > srcutree.c:(.text+0x1b03): undefined reference to `__srcu_read_lock_nmisafe'
    > > > x86_64-linux-gnu-ld: srcutree.c:(.text+0x1b38): undefined reference to `__srcu_read_unlock_nmisafe'
    > > >
    > > > Note that this error is fixed with a later commit:
    > > >
    > > > commit c2d158a284ab ("srcu: Debug NMI safety even on archs that don't
    > > > require it").
    > > >
    > > > This does not affect what I am working on, so feel free to take care of
    > > > it whenever it fits your schedule.
    > >
    > > Good catch, thank you!
    > >
    > > It looks like the first two hunks in include/linux/srcu.h from that
    > > later commit need to be in that earlier commit.
    > >
    > > Frederic, does this make sense, or am I off in the weeds?
    >
    > Actually you need to do that earlier, in
    > 6584822b1be1 ("srcu: Create an srcu_read_lock_nmisafe() and srcu_read_unlock_nmisafe()")
    >
    > This way you don't only fix x86 bisectability but also the one of all the other safe archs.
    >
    > And it's not just the first two hunks, you also need to include
    > the removal of the srcutiny.h/srcutree.h definitions.
    >
    > So namely you need to apply the following to 6584822b1be1. You might
    > meet some minor retro-conflicts (the chknmisafe parameter didn't exist yet),
    > but that's pretty much it:

    Thank you both!

    I have an untested but allegedly fixed branch on -rcu on branch
    srcunmisafe.2022.10.20a.

    Thanx, Paul

    > diff --git a/include/linux/srcu.h b/include/linux/srcu.h
    > index 565f60d57484..f0814ffca34b 100644
    > --- a/include/linux/srcu.h
    > +++ b/include/linux/srcu.h
    > @@ -52,8 +52,6 @@ int init_srcu_struct(struct srcu_struct *ssp);
    > #else
    > /* Dummy definition for things like notifiers. Actual use gets link error. */
    > struct srcu_struct { };
    > -int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, bool chknmisafe) __acquires(ssp);
    > -void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx, bool chknmisafe) __releases(ssp);
    > #endif
    >
    > void call_srcu(struct srcu_struct *ssp, struct rcu_head *head,
    > @@ -66,6 +64,20 @@ unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
    > unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
    > bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
    >
    > +#ifdef CONFIG_NEED_SRCU_NMI_SAFE
    > +int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);
    > +void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);
    > +#else
    > +static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
    > +{
    > + return __srcu_read_lock(ssp);
    > +}
    > +static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
    > +{
    > + __srcu_read_unlock(ssp, idx);
    > +}
    > +#endif /* CONFIG_NEED_SRCU_NMI_SAFE */
    > +
    > #ifdef CONFIG_SRCU
    > void srcu_init(void);
    > #else /* #ifdef CONFIG_SRCU */
    > diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
    > index f890301f123d..f3a4d65b91ef 100644
    > --- a/include/linux/srcutiny.h
    > +++ b/include/linux/srcutiny.h
    > @@ -89,16 +89,4 @@ static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
    > data_race(READ_ONCE(ssp->srcu_idx)),
    > data_race(READ_ONCE(ssp->srcu_idx_max)));
    > }
    > -
    > -static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, bool chknmisafe)
    > -{
    > - BUG();
    > - return 0;
    > -}
    > -
    > -static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx, bool chknmisafe)
    > -{
    > - BUG();
    > -}
    > -
    > #endif
    > diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
    > index 35ffdedf86cc..c689a81752c9 100644
    > --- a/include/linux/srcutree.h
    > +++ b/include/linux/srcutree.h
    > @@ -159,7 +155,4 @@ void synchronize_srcu_expedited(struct srcu_struct *ssp);
    > void srcu_barrier(struct srcu_struct *ssp);
    > void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf);
    >
    > -int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, bool chknmisafe) __acquires(ssp);
    > -void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx, bool chknmisafe) __releases(ssp);
    > -
    > #endif
    >
    >

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