Add generic exit-time stack-depth checking to CONFIG_DEBUG_STACK_USAGE

Add generic exit-time stack-depth checking to CONFIG_DEBUG_STACK_USAGE.

This also adds UML support.

Tested on UML and i386.

[akpm@linux-foundation.org: cleanups, speedups, tweaks]
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/Kconfig.debug

@@ -47,4 +47,13 @@ config GCOV
         If you're involved in UML kernel development and want to use gcov,
         say Y.  If you're unsure, say N.
 
+config DEBUG_STACK_USAGE
+	bool "Stack utilization instrumentation"
+	default N
+	help
+	  Track the maximum kernel stack usage - this will look at each
+	  kernel stack at process exit and log it if it's the deepest
+	  stack seen so far.
+
+	  This option will slow down process creation and destruction somewhat.
 endmenu

arch/um/defconfig

@@ -527,3 +527,4 @@ CONFIG_FORCED_INLINING=y
 # CONFIG_RCU_TORTURE_TEST is not set
 # CONFIG_GPROF is not set
 # CONFIG_GCOV is not set
+# CONFIG_DEBUG_STACK_USAGE is not set

include/asm-um/thread_info.h

@@ -52,10 +52,19 @@ static inline struct thread_info *current_thread_info(void)
 	return ti;
 }
 
+#ifdef CONFIG_DEBUG_STACK_USAGE
+
+#define alloc_thread_info(tsk) \
+	((struct thread_info *) __get_free_pages(GFP_KERNEL | __GFP_ZERO, \
+						 CONFIG_KERNEL_STACK_ORDER))
+#else
+
 /* thread information allocation */
 #define alloc_thread_info(tsk) \
 	((struct thread_info *) __get_free_pages(GFP_KERNEL, \
 						 CONFIG_KERNEL_STACK_ORDER))
+#endif
+
 #define free_thread_info(ti) \
 	free_pages((unsigned long)(ti),CONFIG_KERNEL_STACK_ORDER)
 

kernel/exit.c

@@ -858,6 +858,34 @@ static void exit_notify(struct task_struct *tsk)
 		release_task(tsk);
 }
 
+#ifdef CONFIG_DEBUG_STACK_USAGE
+static void check_stack_usage(void)
+{
+	static DEFINE_SPINLOCK(low_water_lock);
+	static int lowest_to_date = THREAD_SIZE;
+	unsigned long *n = end_of_stack(current);
+	unsigned long free;
+
+	while (*n == 0)
+		n++;
+	free = (unsigned long)n - (unsigned long)end_of_stack(current);
+
+	if (free >= lowest_to_date)
+		return;
+
+	spin_lock(&low_water_lock);
+	if (free < lowest_to_date) {
+		printk(KERN_WARNING "%s used greatest stack depth: %lu bytes "
+				"left\n",
+				current->comm, free);
+		lowest_to_date = free;
+	}
+	spin_unlock(&low_water_lock);
+}
+#else
+static inline void check_stack_usage(void) {}
+#endif
+
 fastcall NORET_TYPE void do_exit(long code)
 {
 	struct task_struct *tsk = current;
@@ -949,6 +977,7 @@ fastcall NORET_TYPE void do_exit(long code)
 	exit_sem(tsk);
 	__exit_files(tsk);
 	__exit_fs(tsk);
+	check_stack_usage();
 	exit_thread();
 	cpuset_exit(tsk);
 	exit_keys(tsk);