PANIC: blockable slep lock (sx) msi @ ....msi.c:374

Scott Long scottl at
Fri May 4 21:57:34 UTC 2007

Julian Elischer wrote:
> John Baldwin wrote:
>> This is wrong because once you do critical_enter(), you are free to 
>> assume that you won't do a context switch until you critical_exit(), 
>> and sx_xlock() would violate that if it blocked on the lock.
> wellllll critical enter doesn't block interupts so it's true if you 
> don't call
> an interrupt as a context switch.
> (it doesn't SWITCH contexts but it does step into a different context.)

Yes, interrupts are serviced when a critical section is entered, but 
ithreads are not run on the same CPU until the critical section is 
exited.  This has been debated quite a bit over the last few years, but
I it's a good compromise.  This implications just don't seem to be 
documented well, especially for those who need a protected, 
uninterruptable context for doing time-critical operations.


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