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SubjectRe: [patch] sys_sync livelock fix
On Tue, 12 Feb 2002, Andrew Morton wrote:

> Thing is, at shutdown all the tasks which are generating write
> traffic should have been killed off, and the filesystems unmounted
> or set readonly. There's no obvious way in which this shutdown
> sequence can be indefinitely stalled by the problem we're discussing here.
>
> If the shutdown scripts are calling sys_sync() *before* killing
> everything then yes, the scripts could hang indefinitely. Is
> this the case?
>
> If "yes" then the scripts are dumb. Just remove the `sync' call.
>
> If "no" then something else is causing the hang.

I recently had the Linux version of Cyclone (usenet transit server) get
unhappy and start growing load without bounds. At L.A. 60 I issued a
killall the the application (which ran on happily), then a killall (-9)
which also didn't kill the processes (there is a problems there, a process
shouldNOT keep running after ill -9!). There a "reboot" which hung, and
finally a "reboot -n" which actually rebooted the machine.

Since -n only means "do sync but don't wait" I have to think that the
problem is not that the script doesn't issue a kill, but that the kill
doesn't work. I think making the sync(2) a single pass write of current
dirty buffers is the only way to avoid stuff like this. making kill -9
work would be great too, there seems to be a long term problem with
threaded programs which are hard to kill.

Just another data point, the bug in this case is not in shutdown.

--
bill davidsen <davidsen@tmr.com>
CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.

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