Deadlocks with recent SMP current

[Julian Elischer]

Robert Watson wrote:
> On Sat, 14 Aug 2004, Jon Noack wrote:
> 
> 
>>Here's a data point:  My dual Pentium3 system has been up for 20+ hours
>>with this patch. Previously, it wouldn't survive for more than an hour
>>or so (regardless of load). 
> 
> 
> Unfortunately, I'm running a box with the same patch and did get a hang.
> The patch appears to correct some known stability issues associated with
> threaded processes, but the build I was using to trigger the hang doesn't
> use threads, so...

Note..
this is understandable

the patch NARROWS a window..
it does not close it..

the more other processes are on teh system the more likely that the
hang will still occur.

the problem is that the critical section holds off the preemption
until teh thread has "PROBABLY" go the KSE back but if it doesn;t get it back,
then the held off preemtion still causes the problem..

we need to somehow alter the [atch so that the critical section is held across 
the cpu_switch.. One possible fix is to make the pre-emption do nothing if
(td->td_kse->ke_thread != td) (where td == curthread)



> 
> Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
> robert at fledge.watson.org      Principal Research Scientist, McAfee Research
> 
> 
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