linux-kernel - Re: why kexec insists on syncing with recent kernels?

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Date:	Fri, 8 Feb 2008 09:53:05 +0100 (CET)
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Tomasz Chmielewski <mangoo@...g.org>
cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: why kexec insists on syncing with recent kernels?

On Thu, 7 Feb 2008, Tomasz Chmielewski wrote:
> According to kernel/kexec.c:
> 
>  * kexec does not sync, or unmount filesystems so if you need
>  * that to happen you need to do that yourself.
> 
> 
> I saw this was true with 2.6.18 kernel (i.e., it didn't sync), but kexec syncs
> with recent kernels (I checked 2.6.23.14 and 2.6.24):
> 
> # kexec -e
> md: stopping all md devices
> sd 2:0:0:0: [sdb] Synchronizing SCSI cache
> 
> 
> With kexec on 2.6.18 it was executing a loaded kernel immediately.
> 
> 
> Generally, it's a good thing to sync before jumping into a new kernel, but it
> breaks my setup here after upgrading from 2.6.18 to 2.6.24.
> 
> Why?
>
> I have a couple of diskless (iSCSI-boot) machines with a buggy BIOS (old
> Supermicro P4SBR/P4SBE) which randomly freeze after rebooting (the machine
> shuts down just fine, but instead of booting again, showing BIOS bootup
> messages etc. you can just see blank screen).
> 
> Therefore, I use kexec as a workaround for this rebooting problem.
> 
> The way kexec works now makes rebooting unreliable again:
> - network interfaces are brought down,
> - kernel tries to sync - it never will, as we're booted off network, which is
> down
> 
> Any ideas why kexec insists on syncing?

kexec calls device_shutdown(), so ->shutdown() will be called for all
devices.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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