PERFORCE change 96128 for review

[John Baldwin]

On Wednesday 26 April 2006 00:28, John Birrell wrote:
> http://perforce.freebsd.org/chv.cgi?CH=96128
> 
> Change 96128 by jb at jb_freebsd2 on 2006/04/26 04:27:13
> 
> 	Update my hacks.
> 	
> 	*HELP*
> 	
> 	This is an area that I will definitely need help with. The function
> 	being executed here needs to be called with pre-emption disabled.
> 	This is being used in the simple case of "dtrace -n BEGIN" (which is
> 	the simplest DTrace you can do), to swap buffers without being
> 	interrupted when it is time to gather up a buffer full and return it
> 	via an ioctl. The buffer change can't be interrupted because that
> 	might allow another probe to add to the buffer that is being uploaded,
> 	causing it to get mis-reported.

I think you can use critical_enter/critical_exit in place of
kpreempt_disable/enable.  They do not block interrupts, but they do defer
context switches (even to interrupt threads) so only INTR_FAST interrupt
handlers will run inside a critical section.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org