linux-kernel - Re: [PATCH] arm64: kexec: flush log to console in nmi

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Message-ID: <CA+CK2bC5XW_AjnieWZ-ro8iqr0Jb7cz5Ss5549tJTq3Zm4GYiQ@mail.gmail.com>
Date:   Thu, 17 Jun 2021 13:55:08 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Will Deacon <will@...nel.org>
Cc:     Huang Shijie <shijie@...amperecomputing.com>,
        Catalin Marinas <catalin.marinas@....com>, tabba@...gle.com,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>, patches@...erecomputing.com,
        zwang@...erecomputing.com
Subject: Re: [PATCH] arm64: kexec: flush log to console in nmi_panic()

On Thu, Jun 17, 2021 at 1:52 PM Will Deacon <will@...nel.org> wrote:
>
> On Thu, Jun 17, 2021 at 12:50:23PM +0000, Huang Shijie wrote:
> > If kdump is configured, nmi_panic() may run to machine_kexec().
> >
> > But in NMI context, the log is put in PER-CPU nmi_print_seq.
> > So we can not see any log on the console since we entered the NMI context,
> > such as the "Bye!" in previous line.
> >
> > This patch fixes this issue by two steps:
> >       1) Uses printk_safe_flush_on_panic() to flush the log from
> >              nmi_print_seq to global printk ring buffer,
> >         2) Then uses console_flush_on_panic() to flush to console.
> >
> > After this patch, we can see the "Bye!" log in the panic console.
>
> Does it matter? I'd be more inclined to remove the print altogether...

I agree, the print could be removed entirely. But, my assumption was
that this patch meant to flush other buffered prints beside this last
"Bye" one.

>
> Will