From:   Thomas Gleixner <tglx@linutronix.de>
To:     David Woodhouse <dwmw2@infradead.org>,
        Usama Arif <usama.arif@bytedance.com>, kim.phillips@amd.com,
        brgerst@gmail.com
Cc:     piotrgorski@cachyos.org, oleksandr@natalenko.name,
        arjan@linux.intel.com, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com, x86@kernel.org,
        pbonzini@redhat.com, paulmck@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        rcu@vger.kernel.org, mimoja@mimoja.de, hewenliang4@huawei.com,
        thomas.lendacky@amd.com, seanjc@google.com, pmenzel@molgen.mpg.de,
        fam.zheng@bytedance.com, punit.agrawal@bytedance.com,
        simon.evans@bytedance.com, liangma@liangbit.com,
        "Guilherme G . Piccoli" <gpiccoli@igalia.com>
Subject: Re: [PATCH v14 10/12] x86/smpboot: Send INIT/SIPI/SIPI to secondary
 CPUs in parallel
In-Reply-To: <5a9d6d4aef78de6fc8a2cfc62922d06617cbe109.camel@infradead.org>
References: <20230308171328.1562857-1-usama.arif@bytedance.com>
 <20230308171328.1562857-11-usama.arif@bytedance.com> <87y1o3acrh.ffs@tglx>
 <5a9d6d4aef78de6fc8a2cfc62922d06617cbe109.camel@infradead.org>
Date:   Sat, 11 Mar 2023 16:14:53 +0200
Message-ID: <87r0tv9xya.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Sat, Mar 11 2023 at 09:55, David Woodhouse wrote:
> On Sat, 2023-03-11 at 10:54 +0200, Thomas Gleixner wrote:
> I think I'll do it with a 'bool unpoison' argument to
> idle_thread_get(). Or just make it unconditional; they're idempotent
> anyway and cheap enough? Kind of weird to be doing it from finish_cpu()
> though, so I'll probably stick with the argument.

Eew.

> ....*types*....
>
> Erm, there are circumstances (!CONFIG_GENERIC_SMP_IDLE_THREAD) when
> idle_thread_get() just unconditionally returns NULL.
>
> At first glance, it doesn't look like scs_task_reset() copes with being
> passed a NULL. Am I missing something?

Shadow call stacks are only enabled by arm64 today, and that uses
the generic idle threads.

Thanks,

        tglx