[IA64] fix interrupt masking for pending works on kernel leave

[Bug-fix for "[BUG?][2.6.25-mm1] sleeping during IRQ disabled"]

This patch does:
 - enable interrupts before calling schedule() as same as others, ex. x86
 - enable interrupts during ia64_do_signal() and ia64_sync_krbs()
 - do_notify_resume_user() is still called with interrupts disabled, since
   we can take short path of fsys_mode if-statement quickly.
 - pfm_handle_work() is also called with interrupts disabled, since
   it can deal interrupt mask within itself.
 - fix/add some comments/notes

Reported-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/entry.S

@@ -1156,6 +1156,9 @@ skip_rbs_switch:
 	 *	r31 = current->thread_info->flags
 	 * On exit:
 	 *	p6 = TRUE if work-pending-check needs to be redone
+	 *
+	 * Interrupts are disabled on entry, reenabled depend on work, and
+	 * disabled on exit.
 	 */
 .work_pending_syscall:
 	add r2=-8,r2
@@ -1170,8 +1173,8 @@ skip_rbs_switch:
 (pKStk) dep r21=-1,r0,PREEMPT_ACTIVE_BIT,1
 	;;
 (pKStk) st4 [r20]=r21
-	ssm psr.i		// enable interrupts
 #endif
+	ssm psr.i		// enable interrupts
 	br.call.spnt.many rp=schedule
 .ret9:	cmp.eq p6,p0=r0,r0				// p6 <- 1
 	rsm psr.i		// disable interrupts
@@ -1234,9 +1237,12 @@ GLOBAL_ENTRY(ia64_invoke_schedule_tail)
 END(ia64_invoke_schedule_tail)
 
 	/*
-	 * Setup stack and call do_notify_resume_user().  Note that pSys and pNonSys need to
-	 * be set up by the caller.  We declare 8 input registers so the system call
-	 * args get preserved, in case we need to restart a system call.
+	 * Setup stack and call do_notify_resume_user(), keeping interrupts
+	 * disabled.
+	 *
+	 * Note that pSys and pNonSys need to be set up by the caller.
+	 * We declare 8 input registers so the system call args get preserved,
+	 * in case we need to restart a system call.
 	 */
 ENTRY(notify_resume_user)
 	.prologue ASM_UNW_PRLG_RP|ASM_UNW_PRLG_PFS, ASM_UNW_PRLG_GRSAVE(8)

arch/ia64/kernel/process.c

@@ -167,28 +167,45 @@ void tsk_clear_notify_resume(struct task_struct *tsk)
 	clear_ti_thread_flag(task_thread_info(tsk), TIF_NOTIFY_RESUME);
 }
 
+/*
+ * do_notify_resume_user():
+ *	Called from notify_resume_user at entry.S, with interrupts disabled.
+ */
 void
-do_notify_resume_user (sigset_t *unused, struct sigscratch *scr, long in_syscall)
+do_notify_resume_user(sigset_t *unused, struct sigscratch *scr, long in_syscall)
 {
 	if (fsys_mode(current, &scr->pt)) {
-		/* defer signal-handling etc. until we return to privilege-level 0.  */
+		/*
+		 * defer signal-handling etc. until we return to
+		 * privilege-level 0.
+		 */
 		if (!ia64_psr(&scr->pt)->lp)
 			ia64_psr(&scr->pt)->lp = 1;
 		return;
 	}
 
 #ifdef CONFIG_PERFMON
 	if (current->thread.pfm_needs_checking)
+		/*
+		 * Note: pfm_handle_work() allow us to call it with interrupts
+		 * disabled, and may enable interrupts within the function.
+		 */
 		pfm_handle_work();
 #endif
 
 	/* deal with pending signal delivery */
-	if (test_thread_flag(TIF_SIGPENDING))
+	if (test_thread_flag(TIF_SIGPENDING)) {
+		local_irq_enable();	/* force interrupt enable */
 		ia64_do_signal(scr, in_syscall);
+	}
 
 	/* copy user rbs to kernel rbs */
-	if (unlikely(test_thread_flag(TIF_RESTORE_RSE)))
+	if (unlikely(test_thread_flag(TIF_RESTORE_RSE))) {
+		local_irq_enable();	/* force interrupt enable */
 		ia64_sync_krbs();
+	}
+
+	local_irq_disable();	/* force interrupt disable */
 }
 
 static int pal_halt        = 1;