sh: Clear UBC when not in use.

This takes care of tearing down the UBC so it's not inadvertently
left configured at the next context switch time. Failure to do
this results in spurious SIGTRAPs in certain debug sequences.
Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/entry-common.S

@@ -224,7 +224,7 @@ work_resched:
 syscall_exit_work:
 	! r0: current_thread_info->flags
 	! r8: current_thread_info
-	tst	#_TIF_SYSCALL_TRACE, r0
+	tst	#_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP, r0
 	bt/s	work_pending
 	 tst	#_TIF_NEED_RESCHED, r0
 #ifdef CONFIG_TRACE_IRQFLAGS

arch/sh/kernel/ptrace.c

@@ -8,7 +8,6 @@
  * SuperH version:   Copyright (C) 1999, 2000  Kaz Kojima & Niibe Yutaka
  *
  */
-
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/mm.h>
@@ -20,8 +19,7 @@
 #include <linux/slab.h>
 #include <linux/security.h>
 #include <linux/signal.h>
-
-#include <asm/io.h>
+#include <linux/io.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
 #include <asm/system.h>
@@ -59,6 +57,23 @@ static inline int put_stack_long(struct task_struct *task, int offset,
 	return 0;
 }
 
+static void ptrace_disable_singlestep(struct task_struct *child)
+{
+	clear_tsk_thread_flag(child, TIF_SINGLESTEP);
+
+	/*
+	 * Ensure the UBC is not programmed at the next context switch.
+	 *
+	 * Normally this is not needed but there are sequences such as
+	 * singlestep, signal delivery, and continue that leave the
+	 * ubc_pc non-zero leading to spurious SIGTRAPs.
+	 */
+	if (child->thread.ubc_pc != 0) {
+		ubc_usercnt -= 1;
+		child->thread.ubc_pc = 0;
+	}
+}
+
 /*
  * Called by kernel/ptrace.c when detaching..
  *
@@ -66,7 +81,7 @@ static inline int put_stack_long(struct task_struct *task, int offset,
  */
 void ptrace_disable(struct task_struct *child)
 {
-	/* nothing to do.. */
+	ptrace_disable_singlestep(child);
 }
 
 long arch_ptrace(struct task_struct *child, long request, long addr, long data)
@@ -156,6 +171,9 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 			set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 		else
 			clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+
+		ptrace_disable_singlestep(child);
+
 		child->exit_code = data;
 		wake_up_process(child);
 		ret = 0;
@@ -171,6 +189,7 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 		ret = 0;
 		if (child->exit_state == EXIT_ZOMBIE)	/* already dead */
 			break;
+		ptrace_disable_singlestep(child);
 		child->exit_code = SIGKILL;
 		wake_up_process(child);
 		break;
@@ -196,6 +215,7 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 			ubc_usercnt += 1;
 		child->thread.ubc_pc = pc;
 
+		set_tsk_thread_flag(child, TIF_SINGLESTEP);
 		child->exit_code = data;
 		/* give it a chance to run. */
 		wake_up_process(child);
@@ -248,14 +268,15 @@ asmlinkage void do_syscall_trace(void)
 {
 	struct task_struct *tsk = current;
 
-	if (!test_thread_flag(TIF_SYSCALL_TRACE))
+	if (!test_thread_flag(TIF_SYSCALL_TRACE) &&
+	    !test_thread_flag(TIF_SINGLESTEP))
 		return;
 	if (!(tsk->ptrace & PT_PTRACED))
 		return;
 	/* the 0x80 provides a way for the tracing parent to distinguish
 	   between a syscall stop and SIGTRAP delivery */
-	ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
-				 ? 0x80 : 0));
+	ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD) &&
+				 !test_thread_flag(TIF_SINGLESTEP) ? 0x80 : 0));
 
 	/*
 	 * this isn't the same as continuing with a signal, but it will do

include/asm-sh/thread_info.h

@@ -111,6 +111,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_SIGPENDING		2	/* signal pending */
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_RESTORE_SIGMASK	4	/* restore signal mask in do_signal() */
+#define TIF_SINGLESTEP		5	/* singlestepping active */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		18
@@ -121,6 +122,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_FREEZE		(1<<TIF_FREEZE)