Prefaulting for i/o buffers

[Konstantin Belousov]

On Sun, Feb 12, 2012 at 10:37:54PM +0200, Ivan Klymenko wrote:
> В Sun, 12 Feb 2012 22:24:13 +0200
> Konstantin Belousov <kostikbel at gmail.com> пишет:
> 
> > On Sun, Feb 12, 2012 at 10:14:56PM +0200, Ivan Klymenko wrote:
> > > В Fri, 3 Feb 2012 21:37:19 +0200
> > > Konstantin Belousov <kostikbel at gmail.com> пишет:
> > > 
> > > > http://people.freebsd.org/~kib/misc/vm1.3.patch
> > > 
> > > I have FreeBSD 10.0-CURRENT #0 r231526M: Sat Feb 11 23:06:18 EET
> > > 2012 ivan at nonamehost:/usr/obj/usr/src/sys/mk10  amd64
> > > 
> > > my system is patched
> > > http://people.freebsd.org/~kib/drm/all.13.2.patch (I do not know is
> > > the important point is whether or not)
> > > 
> > > When using this patch vm1.3.patch or 1.4 or 1.5 or ... including
> > > http://people.freebsd.org/~kib/misc/vm1.9.patch the system works
> > > fine in the console, but when loaded into a graphical environment -
> > > a system gets of global lock (even the mouse cursor does not move)
> > > - only reset helps
> > > 
> > > I'm using Gnome GUI + compiz...
> > 
> > I cannot make anything with this report, since it obviously misses any
> > data on the deadlock.
> 
> Definitely yes :) but
> 
> > 
> > BTW, I just put vm1.10 which allows buildworld over NFS to finish
> > successfully.
> 
> my kernel config file is assembled with the options
> options KDB_TRACE
> options KDB # Enable kernel debugger support.
> options DDB
> also use the patch http://people.freebsd.org/ ~ kib/drm/all.13.2.patch
> where not yet implemented the transition to the console - how do I get
> at least some data using the break-to-debugger Ctrl + Alt + ESC?

Switching the virtual consoles probably would not work on the deadlocked
system anyway, since X server needs to process this operation regardless
of the presence of KMS. The more important, but not yet realized premise
of KMS is the ability to enter the kernel debugger on the graphical console
without switching X session console. But this indeed not implemented.

I suspect that the serial console, or software watchdog and some ddb script
(see ddb(8)) are the only ways forward.
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