s390: TASK_SIZE for kernel threads

Return a sensible value if TASK_SIZE if called from a kernel thread.

This gets us around an issue with copy_mount_options that does a magic
size calculation "TASK_SIZE - (unsigned long)data" while in a kernel
thread and data pointing to kernel space.

Cc: <stable@vger.kernel.org>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index c57c5c2f2484ab821a4f8aec2d4cf05af3209f70..e4988710aa86219a2e4e7e0d9f2338584ae0077a 100644 (file)
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -91,7 +91,8 @@ extern void execve_tail(void);
  * User space process size: 2GB for 31 bit, 4TB or 8PT for 64 bit.
  */
 
-#define TASK_SIZE_OF(tsk)      ((tsk)->mm->context.asce_limit)
+#define TASK_SIZE_OF(tsk)      ((tsk)->mm ? \
+                                (tsk)->mm->context.asce_limit : TASK_MAX_SIZE)
 #define TASK_UNMAPPED_BASE     (test_thread_flag(TIF_31BIT) ? \
                                        (1UL << 30) : (1UL << 41))
 #define TASK_SIZE              TASK_SIZE_OF(current)