linux-kernel - Re: [PATCH] risc-v: Fix order of IPI enablement vs RCU startup

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Date:   Mon, 03 Jul 2023 19:58:03 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Palmer Dabbelt <palmer@...osinc.com>
Cc:     linux-kernel@...r.kernel.org, Conor Dooley <conor@...nel.org>,
        apatel@...tanamicro.com,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] risc-v: Fix order of IPI enablement vs RCU startup

On Mon, 03 Jul 2023 19:45:43 +0100,
Palmer Dabbelt <palmer@...osinc.com> wrote:
> 
> On Mon, 03 Jul 2023 11:31:26 PDT (-0700), Marc Zyngier wrote:
> > Conor reports that risc-v tries to enable IPIs before telling the
> > core code to enable RCU. With the introduction of the mapple tree
> > as a backing store for the irq descriptors, this results in
> > a very shouty boot sequence, as RCU is legitimately upset.
> > 
> > Restore some sanity by moving the risc_ipi_enable() call after
> > notify_cpu_starting(), which explicitly enables RCU on the calling
> > CPU.
> > 
> > Fixes: 832f15f42646 ("RISC-V: Treat IPIs as normal Linux IRQs")
> > Reported-by: Conor Dooley <conor@...nel.org>
> > Signed-off-by: Marc Zyngier <maz@...nel.org>
> > Link: https://lore.kernel.org/r/20230703-dupe-frying-79ae2ccf94eb@spud
> > Cc: Anup Patel <apatel@...tanamicro.com>
> > Cc: Palmer Dabbelt <palmer@...osinc.com>
> > Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> > ---
> >  arch/riscv/kernel/smpboot.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> > index bb0b76e1a6d4..f4d6acb38dd0 100644
> > --- a/arch/riscv/kernel/smpboot.c
> > +++ b/arch/riscv/kernel/smpboot.c
> > @@ -238,10 +238,11 @@ asmlinkage __visible void smp_callin(void)
> >  	mmgrab(mm);
> >  	current->active_mm = mm;
> > 
> > -	riscv_ipi_enable();
> > -
> >  	store_cpu_topology(curr_cpuid);
> >  	notify_cpu_starting(curr_cpuid);
> > +
> > +	riscv_ipi_enable();
> > +
> >  	numa_add_cpu(curr_cpuid);
> >  	set_cpu_online(curr_cpuid, 1);
> >  	probe_vendor_features(curr_cpuid);
> 
> Thanks.  I was going to send another PR this week anyway, I can just
> pick this up if you want?

Yes please!

	M.

-- 
Without deviation from the norm, progress is not possible.