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Re: CVS commit: src/sys/arch/xen/xen

On 12/3/13 12:51 PM, Manuel Bouyer wrote:
Module Name:    src
Committed By:   bouyer
Date:           Tue Dec  3 20:51:00 UTC 2013

Modified Files:
        src/sys/arch/xen/xen: evtchn.c

Log Message:
Remove the "evtchn_do_event: handler %p didn't lower ipl %d %d\n" printf.
With help from Robert Elz we've finally figured out what's going on, and
it actually isn't a bug in the handler, but related to spin mutexes.
When a spin mutex is released, the IPL isn't lowered back if the
curcpu is holding other spin mutexes. This is because mutexes may not
be released in order (and, in this case, the CPU in interrupted while
it holds a spin mutex at IPL < IPL_SCHED).
Also remove the test and resetting the IPL, it will be reset anyway
inside the loop, or at the end of the loop.

Thanks for figuring this one out!  It's been bothering me for a while...


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