X goes blank with SAK SysRq

Raghavendra D Prabhu raghu.prabhu13 at gmail.com
Fri Jan 13 15:37:24 PST 2012


* On Sat, Jan 14, 2012 at 03:57:09AM +0530, Raghavendra D Prabhu <raghu.prabhu13 at gmail.com> wrote:
>When Ctrl-Alt-Bksp (with zapping)  fails to resolve my hang, recently 
>I read about SAK which also works as killing all on current console, 
>and it is invoked as Alt-SysRq-K .
>However, I noticed that invoking it with X running puts the whole 
>system into an unknown state -- blank screen on both monitors with my 
>dual setup -- to be resolved only through REISUB SysRq combination.
>I tried SAK without X running and it works fine with getty respawing. 
>With X running however it goes into above state, unresolvable without 
>a hard reset or REISUB.
>So, is anyone else facing this ? I am running with following 
>X.Org X Server 1.11.3
>Release Date: 2011-12-16
>X Protocol Version 11, Revision 0
>Build Operating System: Linux 3.1.5-1-ARCH x86_64
>Current Operating System: Linux Xye 3.2.0-rc7-VYX #142 SMP PREEMPT Thu 
>Jan 5 19:18:50 IST 2012 x86_64
>Kernel command line: root=/dev/sda6 ro quiet vga=773 devtmpfs.mount=on 
>acpi_osi=Linux intel_iommu=off
>Build Date: 17 December 2011  09:17:41AM
>Current version of pixman: 0.24.0
>        Before reporting problems, check http://wiki.x.org
>                to make sure that you have the latest version.
>Also, the graphics driver is nvidia 295.09.
>There is another way to resolve hung X ie with SysRq-E but it kills 
>all processes (even daemons) except init which I don't want.
>Raghavendra Prabhu
>GPG Id : 0xD72BE977
>Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
>www: wnohang.net

Another thing I noticed is that internally kernel sends a SIGKILL 
to processes when killing them through a __do_SAK, though I see a 
todo over that stating it should first try HUP, then INT and then 
KILL. Also it mentions about potential deadlocks due to interrupt 

Raghavendra Prabhu
GPG Id : 0xD72BE977
Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
www: wnohang.net
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