From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Jinjie Ruan <ruanjinjie@huawei.com>,
Naman Jain <namjain@linux.microsoft.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
Thomas Huth <thuth@redhat.com>, Fuad Tabba <fuad.tabba@linux.dev>,
Thomas Gleixner <tglx@kernel.org>,
Pengjie Zhang <zhangpengjie2@huawei.com>,
mrigendrachaubey <mrigendra.chaubey@gmail.com>,
Saurabh Sengar <ssengar@linux.microsoft.com>
Subject: Re: [PATCH] arm64: smp: distinguish secondary CPUs that hang after reaching head.S
Date: Thu, 23 Jul 2026 11:26:43 +0530 [thread overview]
Message-ID: <70e8596f-7316-4cc9-90e8-ff06a94c4616@arm.com> (raw)
In-Reply-To: <6e13c10f-ccc2-48c3-bf8a-d65133a33e17@huawei.com>
On 23/07/26 8:19 AM, Jinjie Ruan wrote:
>
> 在 2026/7/22 19:30, Naman Jain 写道:
>> When a secondary CPU fails to come online, __cpu_up() falls back to
>> __early_cpu_boot_status, but boot status 0x0 is ambiguous: it cannot
>> distinguish a CPU that never executed head.S (firmware/hypervisor never
>> dispatched it, so it never ran a single instruction) from one that
>> entered head.S, started executing, and then got stuck somewhere in kernel
>> bring-up. Add a change to let us tell those two cases apart, which
>> narrows down where to look when a CPU goes missing during boot.
> I previously encountered this issue when debugging the parallel startup
> of ARM64 secondary cores. It is difficult for the kernel to determine
> whether the secondary core is hung in the firmware or whether it has not
> executed a single instruction. So I think this motive is reasonable.
Why should kernel determine the difference here ? Would not the firmware
know if it has started any secondary CPU for the kernel which must have
come inside head.S ? If the cpu gets hung inside firmware while starting
up then the debug responsibilities belong there instead.
Still wondering what's the rationale for this change.
next prev parent reply other threads:[~2026-07-23 5:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-22 11:30 Naman Jain
2026-07-23 2:49 ` Jinjie Ruan
2026-07-23 5:56 ` Anshuman Khandual [this message]
2026-07-24 4:46 ` Naman Jain
2026-07-24 5:23 ` Anshuman Khandual
2026-07-24 8:01 ` Naman Jain
2026-07-26 13:46 ` Will Deacon
2026-07-27 5:38 ` Naman Jain
2026-08-04 13:43 ` Will Deacon
2026-08-05 4:42 ` Naman Jain
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