From: "Russell King (Oracle)" <linux@armlinux•org.uk>
To: Petr Mladek <pmladek@suse•com>
Cc: Peter Zijlstra <peterz@infradead•org>,
Alexei Starovoitov <ast@kernel•org>,
Chris Wilson <chris@chris-wilson•co.uk>,
"Wolfram Sang \(Renesas\)" <wsa+renesas@sang-engineering•com>,
Paul Mackerras <paulus@samba•org>, Marc Zyngier <maz@kernel•org>,
Masahiro Yamada <masahiroy@kernel•org>,
Ingo Molnar <mingo@redhat•com>,
linux-arm-kernel@lists•infradead.org,
Sami Tolvanen <samitolvanen@google•com>,
Valentin Schneider <valentin.schneider@arm•com>,
Kees Cook <keescook@chromium•org>,
John Ogness <john.ogness@linutronix•de>,
Anshuman Khandual <anshuman.khandual@arm•com>,
Frederic Weisbecker <frederic@kernel•org>,
Steven Rostedt <rostedt@goodmis•org>,
Nathan Chancellor <nathan@kernel•org>,
Nick Terrell <terrelln@fb•com>,
Thomas Gleixner <tglx@linutronix•de>,
Vlastimil Babka <vbabka@suse•cz>,
linux-kernel@vger•kernel.org, Pekka Enberg <penberg@kernel•org>,
Sergey Senozhatsky <senozhatsky@chromium•org>,
Andrew Morton <akpm@linux-foundation•org>,
linuxppc-dev@lists•ozlabs.org, Mike Rapoport <rppt@kernel•org>
Subject: Re: [PATCH printk v3 4/6] printk: remove NMI tracking
Date: Fri, 25 Jun 2021 14:34:25 +0100 [thread overview]
Message-ID: <20210625133425.GX22278@shell.armlinux.org.uk> (raw)
In-Reply-To: <YNXNx68CXrI9QpHD@alley>
On Fri, Jun 25, 2021 at 02:36:23PM +0200, Petr Mladek wrote:
> On Thu 2021-06-24 13:17:46, John Ogness wrote:
> > All NMI contexts are handled the same as the safe context: store the
> > message and defer printing. There is no need to have special NMI
> > context tracking for this. Using in_nmi() is enough.
> >
> > Signed-off-by: John Ogness <john.ogness@linutronix•de>
> > Reviewed-by: Petr Mladek <pmladek@suse•com>
> > ---
> > arch/arm/kernel/smp.c | 2 --
> > arch/powerpc/kexec/crash.c | 3 ---
> > include/linux/hardirq.h | 2 --
> > include/linux/printk.h | 12 ------------
> > init/Kconfig | 5 -----
> > kernel/printk/internal.h | 6 ------
> > kernel/printk/printk_safe.c | 37 +------------------------------------
> > kernel/trace/trace.c | 2 --
> > 8 files changed, 1 insertion(+), 68 deletions(-)
> >
> > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> > index 74679240a9d8..0dd2d733ad62 100644
> > --- a/arch/arm/kernel/smp.c
> > +++ b/arch/arm/kernel/smp.c
> > @@ -668,9 +668,7 @@ static void do_handle_IPI(int ipinr)
> > break;
> >
> > case IPI_CPU_BACKTRACE:
> > - printk_nmi_enter();
> > nmi_cpu_backtrace(get_irq_regs());
> > - printk_nmi_exit();
>
> It looks to me that in_nmi() returns false here. As a result,
> nmi_cpu_backtrace() might newly call consoles immediately.
>
> If I recall correctly, arm does not have a proper NMI.
> And this is just some special case of a "normal" IRQ.
>
> And indeed, nmi_enter() is called only from handle_fiq_as_nmi()
> and it is just a boiler plate.
>
> If I am right, we should replace printk_nmi_enter() with
> printk_safe_enter_irqsave(flags) or so.
>
> Even better solution might be to call this within
> nmi_enter()/nmi_exit(). But I am not sure if this is what
> the arm people want.
As I seem to recall, the guy in ARM Ltd who was working on this seemed
to drift away and it never got finished - however, I've always carried
platform specific hacks in my tree to make this work from FIQ on the
platforms I cared about:
http://git.armlinux.org.uk/cgit/linux-arm.git/commit/?h=fiq
Not suitable for mainline like that. I'm not aware of anyone working on
it now.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
prev parent reply other threads:[~2021-06-25 13:35 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-24 11:11 [PATCH printk v3 0/6] printk: remove safe buffers John Ogness
2021-06-24 11:11 ` [PATCH printk v3 3/6] " John Ogness
2021-06-24 14:49 ` Petr Mladek
2021-06-24 15:35 ` John Ogness
2021-06-25 12:41 ` Petr Mladek
2021-06-24 11:11 ` [PATCH printk v3 4/6] printk: remove NMI tracking John Ogness
2021-06-25 12:36 ` Petr Mladek
2021-06-25 13:34 ` Russell King (Oracle) [this message]
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