Date: Sat, 28 Dec 1996 11:41:51 -0500 From: Michael Petry <petry@netwolf.NetMasters.com> To: freebsd-smp@freebsd.org Cc: louie@wa3ymh.transsys.com Subject: psignal under SMP Message-ID: <199612281641.LAA28588@netwolf.NetMasters.com>
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While showing a buddy the SMP build of FreeBSD we came across an interesting
bug. I opened two windows from my work back to my dual P6-180 system at home.
I compiled the program
main() {
foo:
goto foo;
}
I exec'd it in the second window and was showing that things were still snappy
in the primary window. I then went back to the second window and tried to
kill the process. No go. Hmmm, scratched head and went back to the primary
and ran a few utilities to find out what was going on. Boom!! The process in
the second window dies. My buddy and I kicked the issue around for a while
and then it hit us. The hard cpu process had its signal posted, but never got
rescheduled to see the signals because it was happy and cozy running on the
second processor. My running of some utilities were enough to force it off
its cpu and cause it to be rescheduled and pickup its signal.
Though this is an extreme case (no syscalls , just a hard cpu loop) We thought
some more and concluded that that it would reap havoc with processes that were
computing in wait of a SIGIOs on a relatively idle system.
It looked to us like psignal.c would have to be made smarter to know not only
if a process is runnable, but also if it is running on another CPU and be
IPI'd.
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