From: Baoquan He <bhe@redhat.com>
To: airlied@redhat.com
Cc: kexec@lists.infradead.org, x86@kernel.org,
linux-kernel@vger.kernel.org, dyoung@redhat.com
Subject: Re: mgag200 fails kdump kernel booting
Date: Wed, 26 Jun 2019 16:29:07 +0800 [thread overview]
Message-ID: <20190626082907.GY24419@MiWiFi-R3L-srv> (raw)
In-Reply-To: <20190626081522.GX24419@MiWiFi-R3L-srv>
On 06/26/19 at 04:15pm, Baoquan He wrote:
> Hi Dave,
>
> We met an kdump kernel boot failure on a lenovo system. Kdump kernel
> failed to boot, but just reset to firmware to reboot system. And nothing
> is printed out.
>
> The machine is a big server, with 6T memory and many cpu, its graphic
> driver module is mgag200.
>
> When added 'earlyprintk=ttyS0' into kernel command line, it printed
> out only one line to console during kdump kernel booting:
> KASLR disabled: 'nokaslr' on cmdline.
>
> Then reset to firmware to reboot system.
>
> By further code debugging, the failure happened in
> arch/x86/boot/compressed/misc.c, during kernel decompressing stage. It's
> triggered by the vga printing. As you can see, in __putstr() of
> arch/x86/boot/compressed/misc.c, the code checks if earlyprintk= is
> specified, and print out to the target. And no matter if earlyprintk= is
> added or not, it will print to VGA. And printing to VGA caused it to
> reset to firmware. That's why we see nothing when didn't specify
> earlyprintk=, but see only one line of printing about the 'KASLR
> disabled'.
Here I mean:
That's why we see nothing when didn't specify earlyprintk=, but see only
one line of printing about the 'KASLR disabled' message when
earlyprintk=ttyS0 added.
>
> To confirm it's caused by VGA printing, I blacklist the mgag200 by
> writting it into /etc/modprobe.d/blacklist.conf. The kdump kernel can
> boot up successfully. And add 'nomodeset' can also make it work. So it's
> for sure mgag driver or related code have something wrong when booting
> code tries to re-init it.
>
> This is the only case we ever see, tend to pursuit fix in mgag200 driver
> side. Any idea or suggestion? We have two machines to be able to
> reproduce it stablly.
>
> Thanks
> Baoquan
next prev parent reply other threads:[~2019-06-26 8:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-26 8:15 mgag200 fails kdump kernel booting Baoquan He
2019-06-26 8:29 ` Baoquan He [this message]
2019-07-01 20:51 ` David Airlie
2019-07-02 1:41 ` Baoquan He
2019-07-02 3:17 ` Dave Young
2019-07-02 5:34 ` Baoquan He
2019-07-02 7:42 ` Dave Young
2020-02-05 7:31 ` Baoquan He
2019-07-02 2:21 ` Dave Young
2019-07-02 2:47 ` Baoquan He
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