Re: reentrant probes

["Frank Ch. Eigler" <fche at redhat dot com>]

Hi -

> > [...]  I think it will be quite useful to allow renentrancy in
> > probes.  Not sure why would you want to restrict this.  [...]
> 
> It seems hazardous [...]

I have a different example of the hazards of reentrant probe handling.
Consider a single systemtap session, running

        global a        
        probe kernel.function("foo") { ... a[0] ++ ... }
        probe perfcounter.tlbmiss(20) { ... a[0] ++ ... }

If the perfcounter interrupt is allowed to be taken while the "foo"
probe handler is running and has a lock on the "a" array, then we can
deadlock.


- FChE

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