Re: Deadlocks due to per-process plugging

[Mike Galbraith]

On Wed, 2012-07-18 at 07:30 +0200, Mike Galbraith wrote: 
> On Wed, 2012-07-18 at 06:44 +0200, Mike Galbraith wrote:
> 
> > The patch in question for missing Cc.  Maybe should be only mutex, but I
> > see no reason why IO dependency can only possibly exist for mutexes...
> 
> Well that was easy, box quickly said "nope, mutex only does NOT cut it".

And I also learned (ouch) that both doesn't cut it either.  Ksoftirqd
(or sirq-blk) being nailed by q->lock in blk_done_softirq() is.. not
particularly wonderful.  As long as that doesn't happen, IO deadlock
doesn't happen, troublesome filesystems just work.  If it does happen
though, you've instantly got a problem.

-Mike

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