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From: Nam Cao <namcao@linutronix.de>
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To: litaliano00 <litaliano00.contact@gmail.com>
Cc: palmer@dabbelt.com, pjw@kernel.org, aou@eecs.berkeley.edu,
 alex@ghiti.fr, linux-riscv@lists.infradead.org,
 linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: Add WFI to secondary hart spinwait loop
In-Reply-To: <CAK-CEVO6h+v-2iRdsR6THbOvoTrxM7xnmsDyXfnP5sAgUdmhYQ@mail.gmail.com>
References: <20260407074534.59179-1-litaliano00.contact@gmail.com>
 <20260407084514.syOsks4D@linutronix.de>
 <CAK-CEVO6h+v-2iRdsR6THbOvoTrxM7xnmsDyXfnP5sAgUdmhYQ@mail.gmail.com>
Date: Tue, 07 Apr 2026 13:48:41 +0200
Message-ID: <87tstnuh2e.fsf@yellow.woof>
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litaliano00 <litaliano00.contact@gmail.com> writes:
> You are correct to question this. There is no interrupt sent to the
> waiting harts in the current spinwait design =E2=80=94 the primary hart s=
imply
> writes to __cpu_spinwait_stack_pointer and __cpu_spinwait_task_pointer.
> A bare WFI would cause secondary harts to sleep indefinitely since no
> IPI is issued after those writes.
>
> The correct fix would require the primary hart to send an IPI to all
> waiting harts after populating the pointers, which is a more involved
> change. The current patch is insufficient as-is.

Yeah, that's also what I would do.

> I will send a v2 that reverts this change. Apologies for the noise.

There's no need for that, this patch has not been applied.

Best regards,
Nam