From: Michael Ellerman <mpe@ellerman.id.au>
To: Valentin Schneider <valentin.schneider@arm.com>,
linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
linuxppc-dev@lists.ozlabs.org, linux-kbuild@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Mike Galbraith <efault@gmx.de>, Marco Elver <elver@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Steven Rostedt <rostedt@goodmis.org>,
Masahiro Yamada <masahiroy@kernel.org>,
Michal Marek <michal.lkml@markovi.net>,
Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH v2 3/5] powerpc: Use preemption model accessors
Date: Thu, 11 Nov 2021 15:55:27 +1100 [thread overview]
Message-ID: <87o86rmgu8.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20211110202448.4054153-4-valentin.schneider@arm.com>
Valentin Schneider <valentin.schneider@arm.com> writes:
> Per PREEMPT_DYNAMIC, checking CONFIG_PREEMPT doesn't tell you the actual
> preemption model of the live kernel. Use the newly-introduced accessors
> instead.
>
> sched_init() -> preempt_dynamic_init() happens way before IRQs are set up,
> so this should be fine.
Despite the name interrupt_exit_kernel_prepare() is called before IRQs
are setup, traps and page faults are "interrupts" here.
So I'm not sure about adding that call there, because it will trigger a
WARN if called early in boot, which will trigger a trap and depending on
the context we may not survive.
I'd be happier if we can make it a build-time check.
cheers
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index de10a2697258..c56c10b59be3 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -552,7 +552,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
> /* Returning to a kernel context with local irqs enabled. */
> WARN_ON_ONCE(!(regs->msr & MSR_EE));
> again:
> - if (IS_ENABLED(CONFIG_PREEMPT)) {
> + if (is_preempt_full()) {
> /* Return to preemptible kernel context */
> if (unlikely(current_thread_info()->flags & _TIF_NEED_RESCHED)) {
> if (preempt_count() == 0)
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index aac8c0412ff9..1cb31bbdc925 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -265,7 +265,7 @@ static int __die(const char *str, struct pt_regs *regs, long err)
> printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s %s\n",
> IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? "LE" : "BE",
> PAGE_SIZE / 1024, get_mmu_str(),
> - IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "",
> + is_preempt_full() ? " PREEMPT" : "",
> IS_ENABLED(CONFIG_SMP) ? " SMP" : "",
> IS_ENABLED(CONFIG_SMP) ? (" NR_CPUS=" __stringify(NR_CPUS)) : "",
> debug_pagealloc_enabled() ? " DEBUG_PAGEALLOC" : "",
> --
> 2.25.1
next prev parent reply other threads:[~2021-11-11 4:55 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-10 20:24 [PATCH v2 0/5] preempt: PREEMPT vs PREEMPT_DYNAMIC configs fixup Valentin Schneider
2021-11-10 20:24 ` [PATCH v2 1/5] preempt: Restore preemption model selection configs Valentin Schneider
2021-11-11 8:58 ` Marco Elver
2021-11-11 12:22 ` [tip: sched/urgent] " tip-bot2 for Valentin Schneider
2021-11-10 20:24 ` [PATCH v2 2/5] preempt/dynamic: Introduce preempt mode accessors Valentin Schneider
2021-11-11 3:16 ` Mike Galbraith
2021-11-11 3:35 ` Mike Galbraith
2021-11-11 3:47 ` Mike Galbraith
2021-11-11 3:55 ` Mike Galbraith
2021-11-11 9:36 ` Marco Elver
2021-11-11 10:32 ` Mike Galbraith
2021-11-11 10:56 ` Valentin Schneider
2021-11-11 11:09 ` Mike Galbraith
2021-11-11 8:54 ` Marco Elver
2021-11-11 10:56 ` Valentin Schneider
2021-11-16 13:29 ` Christophe Leroy
2021-11-22 16:37 ` Valentin Schneider
2021-11-10 20:24 ` [PATCH v2 3/5] powerpc: Use preemption model accessors Valentin Schneider
2021-11-11 4:55 ` Michael Ellerman [this message]
2021-11-15 15:29 ` Valentin Schneider
2021-11-16 13:41 ` Christophe Leroy
2021-11-22 16:44 ` Valentin Schneider
2021-11-10 20:24 ` [PATCH v2 4/5] kscan: " Valentin Schneider
2021-11-11 9:11 ` Marco Elver
2021-11-11 9:39 ` Marco Elver
2021-11-11 10:57 ` Valentin Schneider
2021-11-10 20:24 ` [PATCH v2 5/5] ftrace: Use preemption model accessors for trace header printout Valentin Schneider
2021-11-10 20:36 ` Steven Rostedt
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