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From:   John Ogness <john.ogness@linutronix.de>
To:     Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>
Cc:     Luo Jiaxing <luojiaxing@huawei.com>, sergey.senozhatsky@gmail.com,
        rostedt@goodmis.org, linux-kernel@vger.kernel.org,
        linuxarm@huawei.com, bobo.shaobowang@huawei.com
Subject: Re: [PATCH] printk: stop spining waiter when console resume to flush prb
In-Reply-To: <YJkIK9cyHr46UAFP@alley>
References: <1620288026-5373-1-git-send-email-luojiaxing@huawei.com> <YJPxj83F1sBjHHAE@alley> <YJP4F1UIt/eRZ96s@google.com> <YJP5MnkJ8pJevXM6@google.com> <YJVsgPc66lhaAUN0@alley> <YJjuRV57eO3Pp/bp@google.com> <YJkIK9cyHr46UAFP@alley>
Date:   Mon, 10 May 2021 12:32:01 +0200
Message-ID: <871raeop5q.fsf@jogness.linutronix.de>
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On 2021-05-10, Petr Mladek <pmladek@suse.com> wrote:
> The current plan is to move console work to kthreads (separate
> preemptive context). Using IRQ is a complete opposite way.
>
> There is always the fight between getting the messages out as soon
> as possible and the risk of breaking the system (softlockups,
> deadlocks).
>
> The kthread approach reduces the risk of system breakage to a bare
> minimum. The price is that some messages might never reach console.
> There is finally a consensus to give it a try. If it fails, we might
> start looking for alternatives again.

+1

I think it is clear that any such fixups will disappear once
atomic-consoles and console printing kthreads arrive. That doesn't mean
we should ignore the fixups. We just need to decide if it is a real
problem that needs our immediate attention, thus warranting a fixup in
the current implementation.

I can see the suspend/resume issue might be a real problem. If this
should be addressed now, I would support Petr's patch, forcing the
backlog to be printed in the preemptible resuming context. But let's
just keep it a suspend/resume fixup. I do not think we want to start
playing with how console_unlock() behaves.

John Ogness