Kernel/Compiler bug

[Larry Baird]

On Fri, Oct 03, 2014 at 10:35:17AM +0300, Konstantin Belousov wrote:
> I have several notes.  Mostly, it comes from my desire to make the patch
> committable.
I went ahead of made the changes over lunch.  Hopefully the patch below
addresses all of of the issues. Are you able to shepherd this into head or
should I open a PR?

Index: kern_intr.c
===================================================================
--- kern_intr.c	(revision 44897)
+++ kern_intr.c	(working copy)
@@ -1386,6 +1386,14 @@
 	}
 }
 
+#ifdef DEBUG_KERNEL_THREAD_STACK
+static int max_kern_thread_stack_used;
+
+SYSCTL_INT(_kern, OID_AUTO, max_kern_thread_stack_used, CTLFLAG_RD,
+    &max_kern_thread_stack_used, 0,
+    "Maxiumum stack depth used by a kernel thread");
+#endif /* DEBUG_KERNEL_THREAD_STACK */
+
 /*
  * Main interrupt handling body.
  *
@@ -1407,6 +1415,40 @@
 
 	td = curthread;
 
+#ifdef DEBUG_KERNEL_THREAD_STACK
+	/*
+	 * Track maximum stack used by a kernel thread.
+	 *
+	 * Testing for kernel thread isn't strictly needed. It optimizes the
+	 * execution, since interrupts from usermode will have only the trap
+	 * frame on the stack.
+	 */
+	char *bottom_of_stack;
+	char *current;
+	int used;
+
+	if (!TRAPF_USERMODE(frame)) {
+		bottom_of_stack = (char *)(td->td_kstack + td->td_kstack_pages *
+		    PAGE_SIZE - 1);
+		current = (char *)&ih;
+
+		/*
+		 * Try to detect if interrupt is using kernel thread stack.
+		 * Hardware could use a dedicated stack for interrupt handling.
+		 */
+		if (bottom_of_stack > current &&
+		    current > (char *)(td->td_kstack - PAGE_SIZE)) {
+			used = bottom_of_stack - current;
+
+			while (atomic_load_acq_int(&max_kern_thread_stack_used)
+			    < used) {
+				atomic_store_rel_int(&max_kern_thread_stack_used,
+				    used);
+			}
+		}
+	}
+#endif /* DEBUG_KERNEL_THREAD_STACK */
+
 	/* An interrupt with no event or handlers is a stray interrupt. */
 	if (ie == NULL || TAILQ_EMPTY(&ie->ie_handlers))
 		return (EINVAL);

-- 
------------------------------------------------------------------------
Larry Baird
Global Technology Associates, Inc. 1992-2012 	| http://www.gta.com
Celebrating Twenty Years of Software Innovation | Orlando, FL
Email: lab at gta.com                 		| TEL 407-380-0220