Re: What is a livelock? (was: [patch] sys_sync livelock fix)

[Andrew Morton]

Olaf Dietsche wrote:
> 
> Andrew Morton <[e-mail]> writes:
> 
> > The get_request fairness patch exposed a livelock
> > in the buffer layer.  write_unlocked_buffers() will
> > not terminate while other tasks are generating write traffic.
> 
> The subject says it: what is a livelock? How is it different
> from a deadlock?
> 

http://www.huis.hiroshima-u.ac.jp/jargon/LexiconEntries/Livelock.html

livelock

/li:v'lok/ n. A situation in which some critical stage of a task is
unable to finish because its clients perpetually create more work
for it to do after they have been serviced but before it can clear its
queue. Differs from {deadlock} in that the process is not blocked or
waiting for anything, but has a virtually infinite amount of work to
do and can never catch up. 

This exactly describes the sync problem.  But we also use the
term `livelock' to describe one of the Linux VM's favourite
failure modes: madly spinning on page lists and not finding
any useful work to do.  Which is slightly different.

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