[PATCH v2 7/8] alpha: enable lockdep hardirq state tracking

[Magnus Lindholm <linmag7@gmail.com>]

Alpha masks interrupts through the PAL IPL state, so lockdep cannot infer
hardirq state transitions from generic code alone. Add explicit
hardirq on/off annotations to the low-level entry and return paths so
lockdep's IRQ state follows the hardware IPL state.

Annotate the PAL IPL transitions and the shared return-to-user/kernel
paths where interrupts become enabled or disabled.  With the preceding
irqflags, raw-lock, sysfs, and ftrace return-address preparations in
place, select LOCKDEP_SUPPORT and TRACE_IRQFLAGS_SUPPORT for Alpha.

This keeps CONFIG_PROVE_LOCKING usable on Alpha instead of disabling
debug_locks due to IRQ-state mismatches.

Signed-off-by: Magnus Lindholm <linmag7@gmail.com>
---
 .../features/locking/lockdep/arch-support.txt |  2 +-
 arch/alpha/Kconfig                            |  5 ++
 arch/alpha/kernel/entry.S                     | 17 ++++-
 arch/alpha/kernel/irq_alpha.c                 | 74 ++++++++++++++-----
 arch/alpha/kernel/proto.h                     |  4 +
 arch/alpha/kernel/signal.c                    |  9 +++
 6 files changed, 91 insertions(+), 20 deletions(-)

diff --git a/Documentation/features/locking/lockdep/arch-support.txt b/Documentation/features/locking/lockdep/arch-support.txt
index b6b00469f7d0..87a534c89636 100644
--- a/Documentation/features/locking/lockdep/arch-support.txt
+++ b/Documentation/features/locking/lockdep/arch-support.txt
@@ -6,7 +6,7 @@
     -----------------------
     |         arch |status|
     -----------------------
-    |       alpha: | TODO |
+    |       alpha: |  ok  |
     |         arc: |  ok  |
     |         arm: |  ok  |
     |       arm64: |  ok  |
diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 7ac435c56845..e53ef2d88463 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -45,6 +45,8 @@ config ALPHA
 	select MMU_GATHER_RCU_TABLE_FREE
 	select SPARSEMEM_EXTREME if SPARSEMEM
 	select ZONE_DMA
+	select TRACE_IRQFLAGS_SUPPORT
+	select ARCH_WANT_FRAME_POINTERS
 	help
 	  The Alpha is a 64-bit general-purpose processor designed and
 	  marketed by the Digital Equipment Corporation of blessed memory,
@@ -84,6 +86,9 @@ config AUDIT_ARCH
 config STACKTRACE_SUPPORT
 	def_bool y
 
+config LOCKDEP_SUPPORT
+	def_bool y
+
 menu "System setup"
 
 choice
diff --git a/arch/alpha/kernel/entry.S b/arch/alpha/kernel/entry.S
index 449092a31eef..9f2608de2544 100644
--- a/arch/alpha/kernel/entry.S
+++ b/arch/alpha/kernel/entry.S
@@ -93,6 +93,19 @@
 4:
 .endm
 
+.macro LOCKDEP_HARDIRQS_ON_RESTORE
+#ifdef CONFIG_PROVE_LOCKING
+	/* a0 = saved PS */
+	ldq	$16, SP_OFF($sp)
+
+	/* a1 = callsite IP for lockdep */
+	lda	$17, 1f
+
+	jsr	$26, lockdep_on_restore
+	ldgp	$gp, 0($26)
+1:
+#endif
+.endm
 
 /*
  * This defines the normal kernel pt-regs layout.
@@ -427,6 +440,7 @@ CFI_START_OSF_FRAME entUna
 	.cfi_restore	$28
 	.cfi_restore	$29
 	.cfi_adjust_cfa_offset	-256
+	LOCKDEP_HARDIRQS_ON_RESTORE
 	call_pal PAL_rti
 
 	.align	4
@@ -577,6 +591,7 @@ restore_all:
 	bne	$3, restore_fpu
 restore_other:
 	.cfi_remember_state
+	LOCKDEP_HARDIRQS_ON_RESTORE
 	RESTORE_ALL
 	call_pal PAL_rti
 
@@ -622,7 +637,7 @@ $work_resched:
 	 * or got through work_notifysig already.  Either case means no syscall
 	 * restarts for us, so let $18 and $19 burn.
 	 */
-	jsr	$26, schedule
+	jsr	$26, alpha_schedule_user_work
 	mov	0, $18
 	br	ret_to_user
 
diff --git a/arch/alpha/kernel/irq_alpha.c b/arch/alpha/kernel/irq_alpha.c
index d17e44c99df9..736294d3dd51 100644
--- a/arch/alpha/kernel/irq_alpha.c
+++ b/arch/alpha/kernel/irq_alpha.c
@@ -41,7 +41,7 @@ EXPORT_SYMBOL(perf_irq);
  * The main interrupt entry point.
  */
 
-asmlinkage void 
+asmlinkage void
 do_entInt(unsigned long type, unsigned long vector,
 	  unsigned long la_ptr, struct pt_regs *regs)
 {
@@ -54,40 +54,78 @@ do_entInt(unsigned long type, unsigned long vector,
 	 * (namely LX164).
 	 */
 	local_irq_disable();
+	old_regs = set_irq_regs(regs);
+
 	switch (type) {
 	case 0:
 #ifdef CONFIG_SMP
+		irq_enter();
 		handle_ipi(regs);
-		return;
+		irq_exit();
+		break;
 #else
 		irq_err_count++;
-		printk(KERN_CRIT "Interprocessor interrupt? "
-		       "You must be kidding!\n");
-#endif
+		pr_crit("Interprocessor interrupt? You must be kidding!\n");
 		break;
+#endif
 	case 1:
-		old_regs = set_irq_regs(regs);
+		/* handle_irq() already does irq_enter()/irq_exit() */
 		handle_irq(RTC_IRQ);
-		set_irq_regs(old_regs);
-		return;
+		break;
 	case 2:
-		old_regs = set_irq_regs(regs);
+		irq_enter();
 		alpha_mv.machine_check(vector, la_ptr);
-		set_irq_regs(old_regs);
-		return;
+		irq_exit();
+		break;
 	case 3:
-		old_regs = set_irq_regs(regs);
+		irq_enter();
 		alpha_mv.device_interrupt(vector);
-		set_irq_regs(old_regs);
-		return;
+		irq_exit();
+		break;
 	case 4:
+		irq_enter();
 		perf_irq(la_ptr, regs);
-		return;
+		irq_exit();
+		break;
 	default:
-		printk(KERN_CRIT "Hardware intr %ld %lx? Huh?\n",
-		       type, vector);
+		pr_crit("Hardware intr %lu %lx? Huh?\n", type, vector);
+		pr_crit("PC = %016lx PS=%04lx\n", regs->pc, regs->ps);
+		break;
 	}
-	printk(KERN_CRIT "PC = %016lx PS=%04lx\n", regs->pc, regs->ps);
+
+	set_irq_regs(old_regs);
+
+	/*
+	 * Intentionally no local_irq_enable(): Alpha historically avoids
+	 * enabling at IPL0 here due to PAL/RTI issues (LX164/MILO note).
+	 */
+}
+
+void notrace lockdep_on_restore(unsigned long ps,
+				unsigned long ip)
+{
+#ifdef CONFIG_PROVE_LOCKING
+	/* Restoring IPL==7 means interrupts remain disabled. */
+	if ((ps & 7) == 7)
+		return;
+
+	/*
+	 * If hardware IRQs are already enabled here, then emitting a
+	 * hardirqs-on transition is redundant.
+	 */
+	if (!irqs_disabled())
+		return;
+
+	/*
+	 * Only emit the transition if lockdep currently believes
+	 * hardirqs are off.
+	 */
+	if (lockdep_hardirqs_enabled())
+		return;
+
+	lockdep_hardirqs_on_prepare();
+	lockdep_hardirqs_on(ip);
+#endif
 }
 
 void __init
diff --git a/arch/alpha/kernel/proto.h b/arch/alpha/kernel/proto.h
index a8bc3ead776b..9b262ef09a3a 100644
--- a/arch/alpha/kernel/proto.h
+++ b/arch/alpha/kernel/proto.h
@@ -173,6 +173,7 @@ extern void do_sigreturn(struct sigcontext __user *);
 struct rt_sigframe;
 extern void do_rt_sigreturn(struct rt_sigframe __user *);
 extern void do_work_pending(struct pt_regs *, unsigned long, unsigned long, unsigned long);
+extern void alpha_schedule_user_work(void);
 
 /* traps.c */
 extern void dik_show_regs(struct pt_regs *regs, unsigned long *r9_15);
@@ -185,6 +186,9 @@ struct allregs;
 extern void do_entUna(void *, unsigned long, unsigned long, struct allregs *);
 extern void do_entUnaUser(void __user *, unsigned long, unsigned long, struct pt_regs *);
 
+/* irq_alpha.c */
+extern void notrace lockdep_on_restore(unsigned long ps, unsigned long ip);
+
 /* sys_titan.c */
 extern void titan_dispatch_irqs(u64);
 
diff --git a/arch/alpha/kernel/signal.c b/arch/alpha/kernel/signal.c
index e62d1d461b1f..ce40a49b8496 100644
--- a/arch/alpha/kernel/signal.c
+++ b/arch/alpha/kernel/signal.c
@@ -41,6 +41,14 @@ asmlinkage void ret_from_sys_call(void);
  * The OSF/1 sigprocmask calling sequence is different from the
  * C sigprocmask() sequence..
  */
+
+asmlinkage void alpha_schedule_user_work(void)
+{
+	local_irq_enable();
+	schedule();
+	local_irq_disable();
+}
+
 SYSCALL_DEFINE2(osf_sigprocmask, int, how, unsigned long, newmask)
 {
 	sigset_t oldmask;
@@ -525,6 +533,7 @@ do_work_pending(struct pt_regs *regs, unsigned long thread_flags,
 {
 	do {
 		if (thread_flags & _TIF_NEED_RESCHED) {
+			local_irq_enable();
 			schedule();
 		} else {
 			local_irq_enable();
-- 
2.53.0