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Message-ID: <6802d78e-5aeb-6115-a4ec-73be78ccc577@bytedance.com>
Date:   Thu, 7 Jul 2022 21:43:00 +0800
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Subject: Re: [RFC PATCH 1/2] arm64: run softirqs on the per-CPU IRQ stack
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To:     Arnd Bergmann <arnd@arndb.de>
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>
References: <20220707110511.52129-1-zhengqi.arch@bytedance.com>
 <20220707110511.52129-2-zhengqi.arch@bytedance.com>
 <CAK8P3a0h1rFot013raf+O49pvV0JtyBX4Hwp3dt_85jzsJv3ww@mail.gmail.com>
From:   Qi Zheng <zhengqi.arch@bytedance.com>
In-Reply-To: <CAK8P3a0h1rFot013raf+O49pvV0JtyBX4Hwp3dt_85jzsJv3ww@mail.gmail.com>
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On 2022/7/7 20:58, Arnd Bergmann wrote:
> 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.

OK, will do in the next version.

> 
> 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).

I haven't taken a close look at other architectures than x86 and arm,
but I think it's a good idea.

Thanks,
Qi

> 
>          Arnd

-- 
Thanks,
Qi