[Bug 192906] [dtrace] running dtest.pl causes VM to sporadically reboot

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=192906

--- Comment #1 from Garrett Cooper <ngie at FreeBSD.org> ---
Note from Anton Rang @ isilon (Isilon had fixed a similar/potentially same
issue
in 7.x):

From: Rang, Anton
Sent: Thursday, August 21, 2014 11:12 PM
To: 'Cooper, Garrett'
Subject: dtrace bug

When dtrace is running, it’s important that traps be caught by dtrace if
required. This is implemented via hook variables such as dtrace_trap_func and
dtrace_doubletrap_func. However, these can’t be checked from normal C
functions, since dtrace may add a probe at the start of the function, which
causes a trap before the check, which causes an infinite loop.

For dtrace_trap_func, a special trap_check function is used – dtrace knows
about this name and avoids instrumenting it, thus the trap occurs and dtrace is
invoked without an intervening probe.

The same needs to be done for dtrace_dbltrap_func.

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