[PATCH] asm-generic/mmiowb: Get cpu in mmiowb_set_pending

[Emil Renner Berthing]

Hi Ren,

On Sun, 5 Jul 2020 at 16:44, Guo Ren <guoren at kernel.org> wrote:
>
> Hi Emil,
>
> On Sun, Jul 5, 2020 at 10:27 PM Emil Renner Berthing <kernel at esmil.dk> wrote:
> >
> > Without this enabling CONFIG_PREEMPT and CONFIG_DEBUG_PREEMPT
> > results in many errors like this on the HiFive Unleashed
> > RISC-V board:
> >
> > BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
> > caller is regmap_mmio_write32le+0x1c/0x46
> > CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.8.0-rc3-hfu+ #1
> > Call Trace:
> > [<ffffffe000201f6e>] walk_stackframe+0x0/0x7a
> > [<ffffffe0005b290e>] dump_stack+0x6e/0x88
> > [<ffffffe00047365e>] regmap_mmio_write32le+0x18/0x46
> > [<ffffffe0005c4c26>] check_preemption_disabled+0xa4/0xaa
> > [<ffffffe00047365e>] regmap_mmio_write32le+0x18/0x46
> > [<ffffffe0004737c8>] regmap_mmio_write+0x26/0x44
> > [<ffffffe0004715c4>] regmap_write+0x28/0x48
> > [<ffffffe00043dccc>] sifive_gpio_probe+0xc0/0x1da
> > [<ffffffe00000113e>] rdinit_setup+0x22/0x26
> > [<ffffffe000469054>] platform_drv_probe+0x24/0x52
> > [<ffffffe000467e16>] really_probe+0x92/0x21a
> > [<ffffffe0004683a8>] device_driver_attach+0x42/0x4a
> > [<ffffffe0004683ac>] device_driver_attach+0x46/0x4a
> > [<ffffffe0004683f0>] __driver_attach+0x40/0xac
> > [<ffffffe0004683ac>] device_driver_attach+0x46/0x4a
> > [<ffffffe000466a3e>] bus_for_each_dev+0x3c/0x64
> > [<ffffffe000467118>] bus_add_driver+0x11e/0x184
> > [<ffffffe00046889a>] driver_register+0x32/0xc6
> > [<ffffffe00000e5ac>] gpiolib_sysfs_init+0xaa/0xae
> > [<ffffffe0000019ec>] do_one_initcall+0x50/0xfc
> > [<ffffffe00000113e>] rdinit_setup+0x22/0x26
> > [<ffffffe000001bea>] kernel_init_freeable+0x152/0x1da
> > [<ffffffe0005c4d28>] rest_init+0xde/0xe2
> > [<ffffffe0005c4d36>] kernel_init+0xa/0x11a
> > [<ffffffe0005c4d28>] rest_init+0xde/0xe2
> > [<ffffffe000200ff6>] ret_from_syscall_rejected+0x8/0xc
> >
> > Signed-off-by: Emil Renner Berthing <kernel at esmil.dk>
> > ---
> > This patch fixes it, but my guess is that it's not the right
> > fix. Do anyone have a better idea?
> >
> >  include/asm-generic/mmiowb.h | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/asm-generic/mmiowb.h b/include/asm-generic/mmiowb.h
> > index 9439ff037b2d..31a21cdfbbcf 100644
> > --- a/include/asm-generic/mmiowb.h
> > +++ b/include/asm-generic/mmiowb.h
> > @@ -34,8 +34,12 @@ DECLARE_PER_CPU(struct mmiowb_state, __mmiowb_state);
> >
> >  static inline void mmiowb_set_pending(void)
> >  {
> > -       struct mmiowb_state *ms = __mmiowb_state();
> > +       struct mmiowb_state *ms;
> > +
> > +       get_cpu();
> > +       ms = __mmiowb_state();
> >         ms->mmiowb_pending = ms->nesting_count;
> > +       put_cpu();
> >  }
>
> #define __mmiowb_state()        this_cpu_ptr(&__mmiowb_state)
>
> The ptr is a fixed address, so don't worry about the change, and just
> use an atomic_read is enough.
> static inline void mmiowb_set_pending(void)
> {
>         struct mmiowb_state *ms = __mmiowb_state();
> -       ms->mmiowb_pending = ms->nesting_count;
> +      ms->mmiowb_pending = atomic_read(ms->nesting_count);
> }

You may be right, but it doesn't fix the BUG. As far as I can tell it
happens in __mmiowb_state() which expands through this_cpu_ptr and
arch_raw_cpu_ptr to SHIFT_PERCPU_PTR(ptr, __my_cpu_offset), where
__my_cpu_offset is per_cpu_offset(smp_processor_id()) and with
CONFIG_DEBUG_PREEMPT smp_processor_id is actually
debug_smp_processor_id, which eventually checks that preemption is
disabled in check_preemption_disabled.

/Emil
> --
> Best Regards
>  Guo Ren
>
> ML: https://lore.kernel.org/linux-csky/