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>
diff --git a/arch/um/Kconfig.debug b/arch/um/Kconfig.debug
index 09c1aca..c86f5eb 100644
--- a/arch/um/Kconfig.debug
+++ b/arch/um/Kconfig.debug
@@ -47,4 +47,13 @@
         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.
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