[RFC/RFT] calloutng

[Konstantin Belousov]

On Wed, Jan 02, 2013 at 05:22:06PM +0100, Luigi Rizzo wrote:
> On Wed, Jan 02, 2013 at 03:11:05PM +0200, Alexander Motin wrote:
> ...
> > > First of all, if you know that there is already a hardclock/statclock/*
> > > scheduled in [T_X, T_X+D] you just reuse that. This particular bullet
> > > was ""no event scheduled in [T_X, T_X+D]" so you need to generate
> > > a new one.
> > 
> > That is true, but my main point was about merging with external events,
> > which I can't predict and the only way to merge is increase sleep period,
> > hoping for better.
> 
> ok, now i understand why you want to schedule for T_X+D.
> 
> Probably one way to close this discussion would be to provide
> a sysctl so the sysadmin can decide which point in the interval
> to pick when there is no suitable callout already scheduled.
Isn't trying to synchronize to the external events in this way unsafe ?
I remember, but cannot find the reference right now, a scheduler
exploit(s) which completely hide malicious thread from the time
accounting, by making it voluntary yielding right before statclock
should fire. If statistic gathering could be piggy-backed on the
external interrupt, and attacker can control the source of the external
events, wouldn't this give her a handle ?
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