why kexec insists on syncing with recent kernels?

[Tomasz Chmielewski <mangoo@wpkg.org>]

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?


-- 
Tomasz Chmielewski
http://blog.wpkg.org