From: Luming Yu <luyu@redhat.com>
Date: Fri, 9 Nov 2007 12:29:18 +0800
Subject: [ia64] use thread.on_ustack to determine user stack
Message-id: 4733E21E.904@redhat.com
O-Subject: [RHEL 5.2 PATCH] bz253548: Following boot of Montvale - dmesg: Transition failed with error -19
Bugzilla: 253548

bz253548

Description of problem:

The PSR.lp bit of kernel thread kondemand sometimes would be set, then
causes set_pstate PAL call fails with invalid argument. I tracked down
to the place that the PSR.lp was set in do_notify_resume_user.

Upstream status:
The patch proposal has been tested and discussed on mailing list.
http://www.gelato.unsw.edu.au/archives/linux-ia64/0709/21226.html
The only concern is about the possibility of breaking ia64 fast system call.
And the concern has been considered invalid:
http://www.gelato.unsw.edu.au/archives/linux-ia64/0710/21259.html
Specifically for RHEL 5, the ia64 fsys mode __is__ actually __disabled__.
I'm pretty sure the patch will go upstream.

The following back port is tested by me, and it fixes the problem.

Please review, test and AC.

Thanks,
Luming

diff --git a/include/asm-ia64/ptrace.h b/include/asm-ia64/ptrace.h
index 13435f7..414fae3 100644
--- a/include/asm-ia64/ptrace.h
+++ b/include/asm-ia64/ptrace.h
@@ -257,7 +257,7 @@ struct switch_stack {
 # define task_pt_regs(t)		(((struct pt_regs *) ((char *) (t) + IA64_STK_OFFSET)) - 1)
 # define ia64_psr(regs)			((struct ia64_psr *) &(regs)->cr_ipsr)
 # define user_mode(regs)		(((struct ia64_psr *) &(regs)->cr_ipsr)->cpl != 0)
-# define user_stack(task,regs)	((long) regs - (long) task == IA64_STK_OFFSET - sizeof(*regs))
+# define user_stack(task,regs)  (task->thread.on_ustack)
 # define fsys_mode(task,regs)					\
   ({								\
 	  struct task_struct *_task = (task);			\