From: Nick Mathewson <nickm@torproject.org>
Date: Fri, 27 Nov 2009 22:22:19 +0000 (-0500)
Subject: Improved optional lock debugging.
X-Git-Tag: release-2.0.4-alpha~132
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=0cd3bb9f3a53cce9a64ce1536d6e171848e8da59;p=libevent

Improved optional lock debugging.

There were a couple of places in the code where we manually kept lock
counts to make sure we never accessed resources without holding a
lock, and that we never released a lock we didn't have.  The
lock-debugging code already puts counts on _every_ lock when lock
debugging is enabled, so there is no need to keep these counts around
otherwise.  This patch rewrites the ASSERT_FOO_LOCKED macros to all
use a common EVLOCK_ASSERT_LOCKED().

We also teach the lock debugging code to keep track of who exactly
holds each lock, so that EVLOCK_ASSERT_LOCKED() means "locked by this
thread."
---

diff --git a/evbuffer-internal.h b/evbuffer-internal.h
index 2808b6ef..7e08ee9b 100644
--- a/evbuffer-internal.h
+++ b/evbuffer-internal.h
@@ -121,9 +121,6 @@ struct evbuffer {
 	/** Used to implement deferred callbacks. */
 	struct deferred_cb_queue *cb_queue;
 
-	/** For debugging: how many times have we acquired the lock for this
-	 * evbuffer? */
-        int lock_count;
 	/** A reference count on this evbuffer.  When the reference count
 	 * reaches 0, the buffer is destroyed.  Manipulated with
 	 * evbuffer_incref and evbuffer_decref_and_unlock and
@@ -202,47 +199,24 @@ struct evbuffer_chain_reference {
 /** Return a pointer to extra data allocated along with an evbuffer. */
 #define EVBUFFER_CHAIN_EXTRA(t, c) (t *)((struct evbuffer_chain *)(c) + 1)
 
-/** Assert that somebody (hopefully us) is holding the lock on an evbuffer */
+/** Assert that we are holding the lock on an evbuffer */
 #define ASSERT_EVBUFFER_LOCKED(buffer)                  \
-	do {                                            \
-		EVUTIL_ASSERT((buffer)->lock_count > 0);       \
-	} while (0)
-/** Assert that nobody is holding the lock on an evbuffer */
-#define ASSERT_EVBUFFER_UNLOCKED(buffer)                  \
-	do {                                            \
-		EVUTIL_ASSERT((buffer)->lock_count == 0);	\
-	} while (0)
-#define _EVBUFFER_INCREMENT_LOCK_COUNT(buffer)                 \
-	do {                                                   \
-		((struct evbuffer*)(buffer))->lock_count++;    \
-	} while (0)
-#define _EVBUFFER_DECREMENT_LOCK_COUNT(buffer)		      \
-	do {						      \
-		ASSERT_EVBUFFER_LOCKED(buffer);		      \
-		((struct evbuffer*)(buffer))->lock_count--;   \
-	} while (0)
+	EVLOCK_ASSERT_LOCKED((buffer)->lock)
 
 #define EVBUFFER_LOCK(buffer)						\
 	do {								\
 		EVLOCK_LOCK((buffer)->lock, 0);				\
-		_EVBUFFER_INCREMENT_LOCK_COUNT(buffer);			\
 	} while(0)
 #define EVBUFFER_UNLOCK(buffer)						\
 	do {								\
-		_EVBUFFER_DECREMENT_LOCK_COUNT(buffer);			\
 		EVLOCK_UNLOCK((buffer)->lock, 0);			\
 	} while(0)
-
 #define EVBUFFER_LOCK2(buffer1, buffer2)				\
 	do {								\
 		EVLOCK_LOCK2((buffer1)->lock, (buffer2)->lock, 0, 0);	\
-		_EVBUFFER_INCREMENT_LOCK_COUNT(buffer1);		\
-		_EVBUFFER_INCREMENT_LOCK_COUNT(buffer2);		\
 	} while(0)
 #define EVBUFFER_UNLOCK2(buffer1, buffer2)				\
 	do {								\
-		_EVBUFFER_DECREMENT_LOCK_COUNT(buffer1);		\
-		_EVBUFFER_DECREMENT_LOCK_COUNT(buffer2);		\
 		EVLOCK_UNLOCK2((buffer1)->lock, (buffer2)->lock, 0, 0);	\
 	} while(0)
 
diff --git a/evdns.c b/evdns.c
index 1a591700..445a1969 100644
--- a/evdns.c
+++ b/evdns.c
@@ -265,7 +265,6 @@ struct evdns_server_port {
 
 #ifndef _EVENT_DISABLE_THREAD_SUPPORT
 	void *lock;
-	int lock_count;
 #endif
 };
 
@@ -362,7 +361,6 @@ struct evdns_base {
 
 #ifndef _EVENT_DISABLE_THREAD_SUPPORT
 	void *lock;
-	int lock_count;
 #endif
 };
 
@@ -418,22 +416,12 @@ static int strtoint(const char *const str);
 #define EVDNS_UNLOCK(base) _EVUTIL_NIL_STMT
 #define ASSERT_LOCKED(base) _EVUTIL_NIL_STMT
 #else
-#define EVDNS_LOCK(base)						\
-	do {								\
-		if ((base)->lock) {					\
-			EVLOCK_LOCK((base)->lock, 0);			\
-		}							\
-		++(base)->lock_count;					\
-	} while (0)
-#define EVDNS_UNLOCK(base)						\
-	do {								\
-		EVUTIL_ASSERT((base)->lock_count > 0);			\
-		--(base)->lock_count;					\
-		if ((base)->lock) {					\
-			EVLOCK_UNLOCK((base)->lock, 0);			\
-		}							\
-	} while (0)
-#define ASSERT_LOCKED(base) EVUTIL_ASSERT((base)->lock_count > 0)
+#define EVDNS_LOCK(base)			\
+	EVLOCK_LOCK((base)->lock, 0)
+#define EVDNS_UNLOCK(base)			\
+	EVLOCK_UNLOCK((base)->lock, 0)
+#define ASSERT_LOCKED(base)			\
+	EVLOCK_ASSERT_LOCKED((base)->lock)
 #endif
 
 #define CLOSE_SOCKET(s) EVUTIL_CLOSESOCKET(s)
diff --git a/evthread-internal.h b/evthread-internal.h
index b7da22d4..6335a361 100644
--- a/evthread-internal.h
+++ b/evthread-internal.h
@@ -40,6 +40,7 @@ struct event_base;
    enabled. */
 extern struct evthread_lock_callbacks _evthread_lock_fns;
 extern unsigned long (*_evthread_id_fn)(void);
+extern int _evthread_lock_debugging_enabled;
 
 /** True iff the given event_base is set up to use locking */
 #define EVBASE_USING_LOCKS(base)			\
@@ -129,6 +130,18 @@ extern unsigned long (*_evthread_id_fn)(void);
 		if (EVBASE_USING_LOCKS(base))				\
 			_evthread_lock_fns.unlock(0, (base)->lockvar);	\
 	} while (0)
+
+/** If lock debugging is enabled, and lock is non-null, assert that 'lock' is
+ * locked and held by us. */
+#define EVLOCK_ASSERT_LOCKED(lock)					\
+	do {								\
+		if ((lock) && _evthread_lock_debugging_enabled) {	\
+			EVUTIL_ASSERT(_evthread_is_debug_lock_held(lock)); \
+		}							\
+	} while (0)
+
+int _evthread_is_debug_lock_held(void *lock);
+
 #else /* _EVENT_DISABLE_THREAD_SUPPORT */
 
 #define EVTHREAD_GET_ID()	1
@@ -143,7 +156,7 @@ extern unsigned long (*_evthread_id_fn)(void);
 #define EVBASE_IN_THREAD(base)	1
 #define EVBASE_ACQUIRE_LOCK(base, lock) _EVUTIL_NIL_STMT
 #define EVBASE_RELEASE_LOCK(base, lock) _EVUTIL_NIL_STMT
-
+#define EVLOCK_ASSERT_LOCKED(lock) _EVUTIL_NIL_STMT
 #endif
 
 #ifdef __cplusplus
diff --git a/evthread.c b/evthread.c
index 8222ad27..66d7a3dd 100644
--- a/evthread.c
+++ b/evthread.c
@@ -36,6 +36,7 @@
 #include "log-internal.h"
 #include "mm-internal.h"
 #include "util-internal.h"
+#include "evthread-internal.h"
 
 /* globals */
 int _evthread_lock_debugging_enabled = 0;
@@ -150,6 +151,7 @@ evthread_set_lock_create_callbacks(void *(*alloc_fn)(void),
 
 struct debug_lock {
 	unsigned locktype;
+	unsigned long held_by;
 	/* XXXX if we ever use read-write locks, we will need a separate
 	 * lock to protect count. */
 	int count;
@@ -171,6 +173,7 @@ debug_lock_alloc(unsigned locktype)
 	}
 	result->locktype = locktype;
 	result->count = 0;
+	result->held_by = 0;
 	return result;
 }
 
@@ -204,6 +207,13 @@ debug_lock_lock(unsigned mode, void *lock_)
 		++lock->count;
 		if (!(lock->locktype & EVTHREAD_LOCKTYPE_RECURSIVE))
 			EVUTIL_ASSERT(lock->count == 1);
+		if (_evthread_id_fn) {
+			unsigned long me;
+			me = _evthread_id_fn();
+			if (lock->count > 1)
+				EVUTIL_ASSERT(lock->held_by == me);
+			lock->held_by = me;
+		}
 	}
 	return res;
 }
@@ -217,6 +227,12 @@ debug_lock_unlock(unsigned mode, void *lock_)
 		EVUTIL_ASSERT(mode & (EVTHREAD_READ|EVTHREAD_WRITE));
 	else
 		EVUTIL_ASSERT((mode & (EVTHREAD_READ|EVTHREAD_WRITE)) == 0);
+	if (_evthread_id_fn) {
+		unsigned long me = _evthread_id_fn();
+		EVUTIL_ASSERT(lock->held_by == me);
+		if (lock->count == 1)
+			lock->held_by = 0;
+	}
 	--lock->count;
 	EVUTIL_ASSERT(lock->count >= 0);
 	if (_original_lock_fns.unlock)
@@ -244,4 +260,18 @@ evthread_enable_lock_debuging(void)
 	_evthread_lock_debugging_enabled = 1;
 }
 
+int
+_evthread_is_debug_lock_held(void *lock_)
+{
+	struct debug_lock *lock = lock_;
+	if (! lock->count)
+		return 0;
+	if (_evthread_id_fn) {
+		unsigned long me = _evthread_id_fn();
+		if (lock->held_by != me)
+			return 0;
+	}
+	return 1;
+}
+
 #endif