1 files changed, 56 insertions, 11 deletions

diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index 5ac3b547453f..8ce6e7235915 100644
--- a/arch/arc/kernel/process.c
+++ b/arch/arc/kernel/process.c
@@ -47,7 +47,8 @@ SYSCALL_DEFINE0(arc_gettls)
 SYSCALL_DEFINE3(arc_usr_cmpxchg, int *, uaddr, int, expected, int, new)
 {
 	struct pt_regs *regs = current_pt_regs();
-	int uval = -EFAULT;
+	u32 uval;
+	int ret;
 
 	/*
 	 * This is only for old cores lacking LLOCK/SCOND, which by defintion
@@ -60,23 +61,47 @@ SYSCALL_DEFINE3(arc_usr_cmpxchg, int *, uaddr, int, expected, int, new)
 	/* Z indicates to userspace if operation succeded */
 	regs->status32 &= ~STATUS_Z_MASK;
 
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
-		return -EFAULT;
+	ret = access_ok(VERIFY_WRITE, uaddr, sizeof(*uaddr));
+	if (!ret)
+		 goto fail;
 
+again:
 	preempt_disable();
 
-	if (__get_user(uval, uaddr))
-		goto done;
+	ret = __get_user(uval, uaddr);
+	if (ret)
+		 goto fault;
 
-	if (uval == expected) {
-		if (!__put_user(new, uaddr))
-			regs->status32 |= STATUS_Z_MASK;
-	}
+	if (uval != expected)
+		 goto out;
 
-done:
-	preempt_enable();
+	ret = __put_user(new, uaddr);
+	if (ret)
+		 goto fault;
+
+	regs->status32 |= STATUS_Z_MASK;
 
+out:
+	preempt_enable();
 	return uval;
+
+fault:
+	preempt_enable();
+
+	if (unlikely(ret != -EFAULT))
+		 goto fail;
+
+	down_read(&current->mm->mmap_sem);
+	ret = fixup_user_fault(current, current->mm, (unsigned long) uaddr,
+			       FAULT_FLAG_WRITE, NULL);
+	up_read(&current->mm->mmap_sem);
+
+	if (likely(!ret))
+		 goto again;
+
+fail:
+	force_sig(SIGSEGV, current);
+	return ret;
 }
 
 #ifdef CONFIG_ISA_ARCV2
@@ -216,6 +241,26 @@ int copy_thread(unsigned long clone_flags,
 		task_thread_info(current)->thr_ptr;
 	}
 
+
+	/*
+	 * setup usermode thread pointer #1:
+	 * when child is picked by scheduler, __switch_to() uses @c_callee to
+	 * populate usermode callee regs: this works (despite being in a kernel
+	 * function) since special return path for child @ret_from_fork()
+	 * ensures those regs are not clobbered all the way to RTIE to usermode
+	 */
+	c_callee->r25 = task_thread_info(p)->thr_ptr;
+
+#ifdef CONFIG_ARC_CURR_IN_REG
+	/*
+	 * setup usermode thread pointer #2:
+	 * however for this special use of r25 in kernel, __switch_to() sets
+	 * r25 for kernel needs and only in the final return path is usermode
+	 * r25 setup, from pt_regs->user_r25. So set that up as well
+	 */
+	c_regs->user_r25 = c_callee->r25;
+#endif
+
 	return 0;
 }