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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 7 Jul 2022 14:58:21 +0200
Message-ID: <CAK8P3a0h1rFot013raf+O49pvV0JtyBX4Hwp3dt_85jzsJv3ww@mail.gmail.com>
Subject: Re: [RFC PATCH 1/2] arm64: run softirqs on the per-CPU IRQ stack
To:     Qi Zheng <zhengqi.arch@bytedance.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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On Thu, Jul 7, 2022 at 1:05 PM Qi Zheng <zhengqi.arch@bytedance.com> wrote:
>
> Currently arm64 supports per-CPU IRQ stack, but softirqs
> are still handled in the task context.
>
> Since any call to local_bh_enable() at any level in the task's
> call stack may trigger a softirq processing run, which could
> potentially cause a task stack overflow if the combined stack
> footprints exceed the stack's size, let's run these softirqs
> on the IRQ stack as well.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

I think this is the correct approach, but your patch conflicts with another
patch I have queued up in the asm-generic tree, see
https://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic.git/commit/?h=asm-generic&id=f2c5092190f21

Please adapt accordingly.

Are there any architectures left that use IRQ stacks but don't
set HAVE_SOFTIRQ_ON_OWN_STACK? If not, we could
also consider removing the Kconfig symbol and just requiring
it to be done this way (for non-PREEMPT_RT).

        Arnd