Re: [PATCH/RFC] locking/spinlocks: Make __raw_* lock ops static

[Geert Uytterhoeven]

Hi Waiman,

CC s390

On Sun, Mar 3, 2024 at 5:25 AM Waiman Long <longman@xxxxxxxxxx> wrote:
> On 3/1/24 15:43, Geert Uytterhoeven wrote:
> > sh/sdk7786_defconfig (CONFIG_GENERIC_LOCKBREAK=y and
> > CONFIG_DEBUG_LOCK_ALLOC=n):
> >
> > kernel/locking/spinlock.c:68:17: warning: no previous prototype for '__raw_spin_lock' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:80:26: warning: no previous prototype for '__raw_spin_lock_irqsave' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:98:17: warning: no previous prototype for '__raw_spin_lock_irq' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:103:17: warning: no previous prototype for '__raw_spin_lock_bh' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:68:17: warning: no previous prototype for '__raw_read_lock' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:80:26: warning: no previous prototype for '__raw_read_lock_irqsave' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:98:17: warning: no previous prototype for '__raw_read_lock_irq' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:103:17: warning: no previous prototype for '__raw_read_lock_bh' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:68:17: warning: no previous prototype for '__raw_write_lock' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:80:26: warning: no previous prototype for '__raw_write_lock_irqsave' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:98:17: warning: no previous prototype for '__raw_write_lock_irq' [-Wmissing-prototypes]
> > kernel/locking/spinlock.c:103:17: warning: no previous prototype for '__raw_write_lock_bh' [-Wmissing-prototypes]
> >
> > Fix this by making the __raw_* lock ops static.
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> > ---
> > Compile-tested only.
> >
> > Is SH really the only SMP platform where CONFIG_GENERIC_LOCKBREAK=y?
> > ---
> >   kernel/locking/spinlock.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/locking/spinlock.c b/kernel/locking/spinlock.c
> > index 8475a0794f8c5ad2..7009b568e6255d64 100644
> > --- a/kernel/locking/spinlock.c
> > +++ b/kernel/locking/spinlock.c
> > @@ -65,7 +65,7 @@ EXPORT_PER_CPU_SYMBOL(__mmiowb_state);
> >    * towards that other CPU that it should break the lock ASAP.
> >    */
> >   #define BUILD_LOCK_OPS(op, locktype)                                        \
> > -void __lockfunc __raw_##op##_lock(locktype##_t *lock)                        \
> > +static void __lockfunc __raw_##op##_lock(locktype##_t *lock)         \
> >   {                                                                   \
> >       for (;;) {                                                      \
> >               preempt_disable();                                      \
> > @@ -77,7 +77,7 @@ void __lockfunc __raw_##op##_lock(locktype##_t *lock)                       \
> >       }                                                               \
> >   }                                                                   \
> >                                                                       \
> > -unsigned long __lockfunc __raw_##op##_lock_irqsave(locktype##_t *lock)       \
> > +static unsigned long __lockfunc __raw_##op##_lock_irqsave(locktype##_t *lock) \
> >   {                                                                   \
> >       unsigned long flags;                                            \
> >                                                                       \
> > @@ -95,12 +95,12 @@ unsigned long __lockfunc __raw_##op##_lock_irqsave(locktype##_t *lock)    \
> >       return flags;                                                   \
> >   }                                                                   \
> >                                                                       \
> > -void __lockfunc __raw_##op##_lock_irq(locktype##_t *lock)            \
> > +static void __lockfunc __raw_##op##_lock_irq(locktype##_t *lock)     \
> >   {                                                                   \
> >       _raw_##op##_lock_irqsave(lock);                                 \
> >   }                                                                   \
> >                                                                       \
> > -void __lockfunc __raw_##op##_lock_bh(locktype##_t *lock)             \
> > +static void __lockfunc __raw_##op##_lock_bh(locktype##_t *lock)              \
> >   {                                                                   \
> >       unsigned long flags;                                            \
> >                                                                       \
>
> This may not work if CONFIG_GENERIC_LOCKBREAK is defined. We had been

sdk7786_defconfig sets CONFIG_GENERIC_LOCKBREAK=y?

FTR, I checked all defconfigs, and it's set in three of them:
  - s390/debug_defconfig
  - sh/sdk7786_defconfig
  - sh/shx3_defconfig

However, the first one has CONFIG_DEBUG_LOCK_ALLOC=y, so the issue
does not trigger there (but see below).

> talking about taking out CONFIG_GENERIC_LOCKBREAK before. See the thread
> in [1]. However, we didn't proceed further at that time as we weren't
> totally sure if there were still some configurations that required
> CONFIG_GENERIC_LOCKBREAK.
>
> [1] https://lore.kernel.org/lkml/20211022120058.1031690-1-arnd@xxxxxxxxxx/
>
> Anyway, without taking out CONFIG_GENERIC_LOCKBREAK, the proper way to
> fix this issue is probably to declare the proper function prototypes in
> include/linux/rwlock_api_smp.h and include/linux/spinlock_api_smp.h when
> CONFIG_GENERIC_LOCKBREAK is defined.

What is the point of adding function prototypes to header files if the
functions don't seem to be called outside kernel/locking/spinlock.c?
Or is that part of the breakage?

I do not have an sdk7786 or shx3, so I do not know if the kernel
actually boots/works.

The warnings are also seen with s390/debug_defconfig after changing
CONFIG_DEBUG_LOCK_ALLOC=n
CONFIG_DEBUG_WW_MUTEX_SLOWPATH=n
CONFIG_LOCK_STAT=n
CONFIG_PROVE_LOCKING=n
Probably that is the easiest config to test on actual hardware?

Thanks!

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68korg

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