Add stack_save_td_running(), a function to trace the kernel stack of a

running thread.

It is currently implemented only on amd64 and i386; on these
architectures, it is implemented by raising an NMI on the CPU on which
the target thread is currently running. Unlike stack_save_td(), it may
fail, for example if the thread is running in user mode.

This change also modifies the kern.proc.kstack sysctl to use this function,
so that stacks of running threads are shown in the output of "procstat -kk".
This is handy for debugging threads that are stuck in a busy loop.

Reviewed by:	bdrewery, jhb, kib
Sponsored by:	EMC / Isilon Storage Division
Differential Revision:	https://reviews.freebsd.org/D3256

1 files changed, 20 insertions, 11 deletions

diff --git a/sys/i386/i386/trap.c b/sys/i386/i386/trap.c
index a3b1b0d..40f7204 100644
--- a/sys/i386/i386/trap.c
+++ b/sys/i386/i386/trap.c
@@ -50,6 +50,7 @@ __FBSDID("$FreeBSD$");
 #include "opt_isa.h"
 #include "opt_kdb.h"
 #include "opt_npx.h"
+#include "opt_stack.h"
 #include "opt_trap.h"
 
 #include <sys/param.h>
@@ -94,6 +95,7 @@ PMC_SOFT_DEFINE( , , page_fault, write);
 #ifdef SMP
 #include <machine/smp.h>
 #endif
+#include <machine/stack.h>
 #include <machine/tss.h>
 #include <machine/vm86.h>
 
@@ -219,19 +221,26 @@ trap(struct trapframe *frame)
 		goto out;
 	}
 
-#ifdef	HWPMC_HOOKS
-	/*
-	 * CPU PMCs interrupt using an NMI so we check for that first.
-	 * If the HWPMC module is active, 'pmc_hook' will point to
-	 * the function to be called.  A return value of '1' from the
-	 * hook means that the NMI was handled by it and that we can
-	 * return immediately.
-	 */
-	if (type == T_NMI && pmc_intr &&
-	    (*pmc_intr)(PCPU_GET(cpuid), frame))
-	    goto out;
+	if (type == T_NMI) {
+#ifdef HWPMC_HOOKS
+		/*
+		 * CPU PMCs interrupt using an NMI so we check for that first.
+		 * If the HWPMC module is active, 'pmc_hook' will point to
+		 * the function to be called.  A non-zero return value from the
+		 * hook means that the NMI was consumed by it and that we can
+		 * return immediately.
+		 */
+		if (pmc_intr != NULL &&
+		    (*pmc_intr)(PCPU_GET(cpuid), frame) != 0)
+			goto out;
 #endif
 
+#ifdef STACK
+		if (stack_nmi_handler(frame) != 0)
+			goto out;
+#endif
+	}
+
 	if (type == T_MCHK) {
 		mca_intr();
 		goto out;