4 files changed, 48 insertions, 0 deletions

diff --git a/arch/um/Kconfig.debug b/arch/um/Kconfig.debug
index 09c1aca6339f..c86f5eb29fd5 100644
--- a/arch/um/Kconfig.debug
+++ b/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
diff --git a/arch/um/defconfig b/arch/um/defconfig
index a54d0efecae1..e5b2df9e12de 100644
--- a/arch/um/defconfig
+++ b/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
diff --git a/include/asm-um/thread_info.h b/include/asm-um/thread_info.h
index 07aa4e50e4d0..6e5fd5c892d0 100644
--- a/include/asm-um/thread_info.h
+++ b/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)
 
diff --git a/kernel/exit.c b/kernel/exit.c
index ca6a11b73023..64a5263c8c7b 100644
--- a/kernel/exit.c
+++ b/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);