libctdb: use magic to detect free/invalid locks

Rather than using a binary, we use a magic value for locking.  We also
split out the "dont have the lock yet" from the "do have the lock"
paths for clarity and extra checking.

This should detect a superset of the previous case, even if they free
(and reuse) the lock memory.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/libctdb/ctdb.c b/libctdb/ctdb.c
index b7f1c590e0d3eb050ed1f6f9f82071b3366c33da..11f0549647c42fbad39aedb2ea9b40b1c278da25 100644 (file)
--- a/libctdb/ctdb.c
+++ b/libctdb/ctdb.c
@@ -42,8 +42,8 @@ struct ctdb_lock {
        struct ctdb_db *ctdb_db;
        TDB_DATA key;
 
-       /* This will always be true by the time user sees this. */
-       bool held;
+       /* This will always be set by the time user sees this. */
+       unsigned long held_magic;
        struct ctdb_ltdb_header *hdr;
 
        /* For convenience, we stash original callback here. */
@@ -633,35 +633,43 @@ ctdb_attachdb_send(struct ctdb_connection *ctdb,
        return req;
 }
 
-void ctdb_release_lock(struct ctdb_lock *lock)
+static unsigned long lock_magic(struct ctdb_lock *lock)
 {
-       if (lock->held) {
-               tdb_chainunlock(lock->ctdb_db->tdb, lock->key);
-               DEBUG(lock->ctdb_db->ctdb, LOG_DEBUG,
-                     "ctdb_release_lock %p", lock);
-               lock->held = false;
-               remove_lock(lock->ctdb_db->ctdb, lock);
-       }
+       /* A non-zero magic specific to this structure. */
+       return ((unsigned long)lock->key.dptr
+               ^ (((unsigned long)lock->key.dptr) << 16)
+               ^ 0xBADC0FFEEBADC0DEULL)
+               | 1;
 }
 
-static void ctdb_free_lock(struct ctdb_lock *lock)
+/* This is only called on locks before they're held. */
+static void free_lock(struct ctdb_lock *lock)
 {
-       if (lock->held) {
-               errno = EEXIST;
-               DEBUG(lock->ctdb_db->ctdb, LOG_ERR,
-                       "Lock freed before it was released");
-               ctdb_release_lock(lock);
+       if (lock->held_magic) {
+               DEBUG(lock->ctdb_db->ctdb, LOG_CRIT,
+                     "free_lock invalid lock %p", lock);
        }
        free(lock->hdr);
        free(lock);
 }
 
-static void ctdb_destroy_lock(struct ctdb_lock *lock)
+
+void ctdb_release_lock(struct ctdb_lock *lock)
 {
-       ctdb_release_lock(lock);
-       ctdb_free_lock(lock);
+       if (lock->held_magic != lock_magic(lock)) {
+               DEBUG(lock->ctdb_db->ctdb, LOG_CRIT,
+                     "ctdb_release_lock invalid lock %p", lock);
+       } else {
+               tdb_chainunlock(lock->ctdb_db->tdb, lock->key);
+               DEBUG(lock->ctdb_db->ctdb, LOG_DEBUG,
+                     "ctdb_release_lock %p", lock);
+               remove_lock(lock->ctdb_db->ctdb, lock);
+       }
+       lock->held_magic = 0;
+       free_lock(lock);
 }
 
+
 /* We keep the lock if local node is the dmaster. */
 static bool try_readrecordlock(struct ctdb_lock *lock, TDB_DATA *data)
 {
@@ -677,7 +685,7 @@ static bool try_readrecordlock(struct ctdb_lock *lock, TDB_DATA *data)
        if (hdr && hdr->dmaster == lock->ctdb_db->ctdb->pnn) {
                DEBUG(lock->ctdb_db->ctdb, LOG_DEBUG,
                      "ctdb_readrecordlock_async: got local lock");
-               lock->held = true;
+               lock->held_magic = lock_magic(lock);
                lock->hdr = hdr;
                add_lock(lock->ctdb_db->ctdb, lock);
                return true;
@@ -692,7 +700,7 @@ static bool try_readrecordlock(struct ctdb_lock *lock, TDB_DATA *data)
 static void destroy_lock(struct ctdb_connection *ctdb,
                         struct ctdb_request *req)
 {
-       ctdb_destroy_lock(req->extra);
+       free_lock(req->extra);
 }
 
 static void readrecordlock_retry(struct ctdb_connection *ctdb,
@@ -720,7 +728,6 @@ static void readrecordlock_retry(struct ctdb_connection *ctdb,
                /* Now it's their responsibility to free lock & request! */
                req->extra_destructor = NULL;
                lock->callback(lock->ctdb_db, lock, data, private);
-               ctdb_free_lock(lock);
                return;
        }
 
@@ -755,12 +762,11 @@ ctdb_readrecordlock_async(struct ctdb_db *ctdb_db, TDB_DATA key,
        lock->key.dsize = key.dsize;
        lock->ctdb_db = ctdb_db;
        lock->hdr = NULL;
-       lock->held = false;
+       lock->held_magic = 0;
 
        /* Fast path. */
        if (try_readrecordlock(lock, &data)) {
                callback(ctdb_db, lock, data, cbdata);
-               ctdb_free_lock(lock);
                return true;
        }
 
@@ -770,7 +776,7 @@ ctdb_readrecordlock_async(struct ctdb_db *ctdb_db, TDB_DATA key,
        if (!req) {
                DEBUG(ctdb_db->ctdb, LOG_ERR,
                      "ctdb_readrecordlock_async: allocation failed");
-               ctdb_destroy_lock(lock);
+               free_lock(lock);
                return NULL;
        }
        req->extra = lock;
@@ -794,7 +800,7 @@ ctdb_readrecordlock_async(struct ctdb_db *ctdb_db, TDB_DATA key,
 
 int ctdb_writerecord(struct ctdb_lock *lock, TDB_DATA data)
 {
-       if (!lock->held) {
+       if (lock->held_magic != lock_magic(lock)) {
                errno = EBADF;
                DEBUG(lock->ctdb_db->ctdb, LOG_ERR,
                      "ctdb_writerecord: Can not write. Lock has been released.");