[IA64] MCA recovery improvements

Jack Steiner uncovered some opportunities for improvement in
the MCA recovery code.

  1) Set bsp to save registers on the kernel stack.
  2) Disable interrupts while in the MCA recovery code.
  3) Change the way the user process is killed, to avoid 
     a panic in schedule.

Testing shows that these changes make the recovery code much 
more reliable with the 2.6.12 kernel.
Signed-off-by: Russ Anderson <rja@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/mca_drv.c

@@ -132,8 +132,7 @@ mca_handler_bh(unsigned long paddr)
 	spin_unlock(&mca_bh_lock);
 
 	/* This process is about to be killed itself */
-	force_sig(SIGKILL, current);
-	schedule();
+	do_exit(SIGKILL);
 }
 
 /**
@@ -439,6 +438,7 @@ recover_from_read_error(slidx_table_t *slidx, peidx_table_t *peidx, pal_bus_chec
 			psr2 = (struct ia64_psr *)&pmsa->pmsa_ipsr;
 			psr2->cpl = 0;
 			psr2->ri  = 0;
+			psr2->i  = 0;
 
 			return 1;
 		}

arch/ia64/kernel/mca_drv_asm.S

@@ -10,6 +10,7 @@
 
 #include <asm/asmmacro.h>
 #include <asm/processor.h>
+#include <asm/ptrace.h>
 
 GLOBAL_ENTRY(mca_handler_bhhook)
 	invala						// clear RSE ?
@@ -20,12 +21,21 @@ GLOBAL_ENTRY(mca_handler_bhhook)
 	;;						
 	alloc		r16=ar.pfs,0,2,1,0		// make a new frame
 	;;
+	mov		ar.rsc=0
+	;;
 	mov		r13=IA64_KR(CURRENT)		// current task pointer
 	;;
-	adds		r12=IA64_TASK_THREAD_KSP_OFFSET,r13
+	mov		r2=r13
+	;;
+	addl		r22=IA64_RBS_OFFSET,r2
+	;;
+	mov		ar.bspstore=r22
 	;;
-	ld8		r12=[r12]			// stack pointer
+	addl		sp=IA64_STK_OFFSET-IA64_PT_REGS_SIZE,r2
 	;;
+	adds		r2=IA64_TASK_THREAD_ON_USTACK_OFFSET,r13
+	;;
+	st1		[r2]=r0				// clear current->thread.on_ustack flag
 	mov		loc0=r16
 	movl		loc1=mca_handler_bh		// recovery C function
 	;;
@@ -34,7 +44,9 @@ GLOBAL_ENTRY(mca_handler_bhhook)
 	;;
 	mov		loc1=rp
 	;;
-	br.call.sptk.many    rp=b6			// not return ...
+	ssm		psr.i
+	;;
+	br.call.sptk.many    rp=b6			// does not return ...
 	;;
 	mov		ar.pfs=loc0
 	mov 		rp=loc1