From 534879b0c068189d2e8155f390f0b5b0724e8861 Mon Sep 17 00:00:00 2001
From: Ali Mashtizadeh <mashti@cs.stanford.edu>
Date: Thu, 22 Jan 2015 13:52:02 -0800
Subject: [PATCH] Show lock stack when a spinlock waits too long

---
 sys/include/spinlock.h |  1 +
 sys/kern/spinlock.c    | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/sys/include/spinlock.h b/sys/include/spinlock.h
index 495879a..dccda9a 100644
--- a/sys/include/spinlock.h
+++ b/sys/include/spinlock.h
@@ -16,6 +16,7 @@ typedef struct Spinlock
     uint64_t		    lockedTSC;
     char		    name[SPINLOCK_NAMELEN];
     LIST_ENTRY(Spinlock)    lockList;
+    TAILQ_ENTRY(Spinlock)   lockStack;
 } Spinlock;
 
 void Critical_Init();
diff --git a/sys/kern/spinlock.c b/sys/kern/spinlock.c
index f329a90..6a811a8 100644
--- a/sys/kern/spinlock.c
+++ b/sys/kern/spinlock.c
@@ -11,10 +11,14 @@
 #include <sys/spinlock.h>
 
 #include <machine/atomic.h>
+#include <machine/amd64.h>
+#include <machine/amd64op.h>
 
 Spinlock lockListLock = { 0, 0, 0, 0, 0, 0, "SPINLOCK LIST" };
 LIST_HEAD(LockListHead, Spinlock) lockList = LIST_HEAD_INITIALIZER(lockList);
 
+TAILQ_HEAD(LockStack, Spinlock) lockStack = TAILQ_HEAD_INITIALIZER(lockStack);
+
 extern uint64_t ticksPerSecond;
 
 void
@@ -52,6 +56,7 @@ Spinlock_Lock(Spinlock *lock)
     {
 	if ((Time_GetTSC() - startTSC) / ticksPerSecond > 1) {
 	    kprintf("Spinlock_Lock(%s): waiting for over a second!\n", lock->name);
+	    breakpoint();
 	}
     }
     lock->waitTime += Time_GetTSC() - startTSC;
@@ -59,11 +64,15 @@ Spinlock_Lock(Spinlock *lock)
     lock->cpu = CPU();
     lock->count++;
     lock->lockedTSC = Time_GetTSC();
+
+    TAILQ_INSERT_TAIL(&lockStack, lock, lockStack);
 }
 
 void
 Spinlock_Unlock(Spinlock *lock)
 {
+    TAILQ_REMOVE(&lockStack, lock, lockStack);
+
     lock->cpu = 0;
     lock->lockTime += Time_GetTSC() - lock->lockedTSC;
     
@@ -98,3 +107,16 @@ Debug_Spinlocks(int argc, const char *argv[])
 
 REGISTER_DBGCMD(spinlocks, "Display list of spinlocks", Debug_Spinlocks);
 
+void
+Debug_LockStack(int argc, const char *argv[])
+{
+    Spinlock *lock;
+
+    kprintf("Lock Stack:\n");
+    TAILQ_FOREACH(lock, &lockStack, lockStack) {
+	kprintf("    %s\n", lock->name);
+    }
+}
+
+REGISTER_DBGCMD(lockstack, "Display stack of held spinlocks", Debug_LockStack);
+