From: Huang Shijie <shijie@os.amperecomputing.com>
To: Will Deacon <will@kernel.org>
Cc: Pavel Tatashin <pasha.tatashin@soleen.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: Tue, 22 Jun 2021 10:14:38 +0000 [thread overview]
Message-ID: <YNG4DgMPluU9T9+R@hsj> (raw)
In-Reply-To: <20210621100836.GA28788@willie-the-truck>
Hi Will,
On Mon, Jun 21, 2021 at 11:08:37AM +0100, Will Deacon wrote:
> > > 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?)
> > In the non-kdump code path, the core code will take care of it, please read the
> > code in panic().
> >
> > But in the kdump code path, the architecture code should take care of it.
>
> Why the discrepancy? Wouldn't it make more sense to do this in panic() for
> both cases, if the prints that we want to display are coming from panic()
> itself?
In the kdump code path, code call like this:
panic() -->__crash_kexec() --> machine_kexec();
When we reach arm64's machine_kexec(), it means we can __NOT__ return to the panic(), we will run
to the kdump linux kernel by cpu_soft_restart().
So we can not depend the panic() to print the log. :)
By the way, I quote part of the arm64 log after we enter __crash_kexec() in NMI context:
1.) the log in machine_crash_shutdown()
..............
pr_crit("SMP: stopping secondary CPUs\n");
..............
pr_info("Starting crashdump kernel...\n");
..............
2.) the log in machine_kexec()
..............
WARN(in_kexec_crash && (stuck_cpus || smp_crash_stop_failed()),
"Some CPUs may be stale, kdump will be unreliable.\n");
..............
the logs in kexec_segment_flush(kimage);
..............
pr_info("Bye!\n");
We cannot remove them all, and need to flush all the logs above to console in the NMI context.
Thanks
Huang Shijie
prev parent reply other threads:[~2021-06-22 2:15 UTC|newest]
Thread overview: 7+ 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 17:52 ` Will Deacon
2021-06-17 17:55 ` Pavel Tatashin
2021-06-17 17:58 ` Will Deacon
2021-06-18 9:03 ` Huang Shijie
2021-06-21 10:08 ` Will Deacon
2021-06-22 10:14 ` Huang Shijie [this message]
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