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From: Will Deacon <will@kernel.org>
To: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Huang Shijie <shijie@os.amperecomputing.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	tabba@google.com, Ard Biesheuvel <ardb@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	patches@amperecomputing.com, zwang@amperecomputing.com
Subject: Re: [PATCH] arm64: kexec: flush log to console in nmi_panic()
Date: Thu, 17 Jun 2021 18:58:23 +0100	[thread overview]
Message-ID: <20210617175822.GG24813@willie-the-truck> (raw)
In-Reply-To: <CA+CK2bC5XW_AjnieWZ-ro8iqr0Jb7cz5Ss5549tJTq3Zm4GYiQ@mail.gmail.com>

On Thu, Jun 17, 2021 at 01:55:08PM -0400, Pavel Tatashin wrote:
> On Thu, Jun 17, 2021 at 1:52 PM Will Deacon <will@kernel.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.

That sounds like something which should be done in the core code, rather
than the in the architecture backend (and looks like panic() might do this
already?)

Will

WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will@kernel.org>
To: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Huang Shijie <shijie@os.amperecomputing.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	tabba@google.com, Ard Biesheuvel <ardb@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	patches@amperecomputing.com, zwang@amperecomputing.com
Subject: Re: [PATCH] arm64: kexec: flush log to console in nmi_panic()
Date: Thu, 17 Jun 2021 18:58:23 +0100	[thread overview]
Message-ID: <20210617175822.GG24813@willie-the-truck> (raw)
In-Reply-To: <CA+CK2bC5XW_AjnieWZ-ro8iqr0Jb7cz5Ss5549tJTq3Zm4GYiQ@mail.gmail.com>

On Thu, Jun 17, 2021 at 01:55:08PM -0400, Pavel Tatashin wrote:
> On Thu, Jun 17, 2021 at 1:52 PM Will Deacon <will@kernel.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.

That sounds like something which should be done in the core code, rather
than the in the architecture backend (and looks like panic() might do this
already?)

Will

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  reply	other threads:[~2021-06-17 17:58 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-17 12:50 [PATCH] arm64: kexec: flush log to console in nmi_panic() Huang Shijie
2021-06-17 12:50 ` Huang Shijie
2021-06-17 17:52 ` Will Deacon
2021-06-17 17:52   ` Will Deacon
2021-06-17 17:55   ` Pavel Tatashin
2021-06-17 17:55     ` Pavel Tatashin
2021-06-17 17:58     ` Will Deacon [this message]
2021-06-17 17:58       ` Will Deacon
2021-06-18  9:03       ` Huang Shijie
2021-06-18  9:03         ` Huang Shijie
2021-06-21 10:08         ` Will Deacon
2021-06-21 10:08           ` Will Deacon
2021-06-22 10:14           ` Huang Shijie
2021-06-22 10:14             ` Huang Shijie

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