tdb: use tdb_lockall_gradual by default.

This has the advantage the transactions will also use it, preventing them
from blocking.

ccan/tdb/lock.c

@@ -152,14 +152,6 @@ int tdb_brlock(struct tdb_context *tdb,
 		return -1;
 	}
 
-	/* Sanity check */
-	if (tdb->transaction && offset >= lock_offset(-1) && len != 0) {
-		tdb->ecode = TDB_ERR_RDONLY;
-		TDB_LOG((tdb, TDB_DEBUG_TRACE, "tdb_brlock attempted in transaction at offset %d rw_type=%d flags=%d len=%d\n",
-			 offset, rw_type, flags, (int)len));
-		return -1;
-	}
-
 	do {
 		ret = fcntl_lock(tdb, rw_type, offset, len,
 				 flags & TDB_LOCK_WAIT);
@@ -520,8 +512,43 @@ static int tdb_allrecord_check(struct tdb_context *tdb, int ltype,
 	return 1;
 }
 
+/* We only need to lock individual bytes, but Linux merges consecutive locks
+ * so we lock in contiguous ranges. */
+static int tdb_chainlock_gradual(struct tdb_context *tdb,
+				 int ltype, enum tdb_lock_flags flags,
+				 size_t off, size_t len)
+{
+	int ret;
+	enum tdb_lock_flags nb_flags = (flags & ~TDB_LOCK_WAIT);
+
+	if (len <= 4) {
+		/* Single record.  Just do blocking lock. */
+		return tdb_brlock(tdb, ltype, off, len, flags);
+	}
+
+	/* First we try non-blocking. */
+	ret = tdb_brlock(tdb, ltype, off, len, nb_flags);
+	if (ret == 0) {
+		return 0;
+	}
+
+	/* Try locking first half, then second. */
+	ret = tdb_chainlock_gradual(tdb, ltype, flags, off, len / 2);
+	if (ret == -1)
+		return -1;
+
+	ret = tdb_chainlock_gradual(tdb, ltype, flags,
+				    off + len / 2, len - len / 2);
+	if (ret == -1) {
+		tdb_brunlock(tdb, ltype, off, len / 2);
+		return -1;
+	}
+	return 0;
+}
+
 /* lock/unlock entire database.  It can only be upgradable if you have some
- * other way of guaranteeing exclusivity (ie. transaction write lock). */
+ * other way of guaranteeing exclusivity (ie. transaction write lock).
+ * We do the locking gradually to avoid being starved by smaller locks. */
 int tdb_allrecord_lock(struct tdb_context *tdb, int ltype,
 		       enum tdb_lock_flags flags, bool upgradable)
 {
@@ -532,10 +559,23 @@ int tdb_allrecord_lock(struct tdb_context *tdb, int ltype,
 		return 0;
 	}
 
-	if (tdb_brlock(tdb, ltype, FREELIST_TOP, 0, flags)) {
-		if (flags & TDB_LOCK_WAIT) {
-			TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_lockall failed (%s)\n", strerror(errno)));
-		}
+	/* We cover two kinds of locks:
+	 * 1) Normal chain locks.  Taken for almost all operations.
+	 * 3) Individual records locks.  Taken after normal or free
+	 *    chain locks.
+	 *
+	 * It is (1) which cause the starvation problem, so we're only
+	 * gradual for that. */
+	if (tdb_chainlock_gradual(tdb, ltype, flags, FREELIST_TOP,
+				  tdb->header.hash_size * 4) == -1) {
+		return -1;
+	}
+
+	/* Grab individual record locks. */
+	if (tdb_brlock(tdb, ltype, lock_offset(tdb->header.hash_size), 0,
+		       flags) == -1) {
+		tdb_brunlock(tdb, ltype, FREELIST_TOP,
+			     tdb->header.hash_size * 4);
 		return -1;
 	}
 
@@ -660,85 +700,6 @@ int tdb_unlockall_read(struct tdb_context *tdb)
 	return tdb_allrecord_unlock(tdb, F_RDLCK, false);
 }
 
-/* We only need to lock individual bytes, but Linux merges consecutive locks
- * so we lock in contiguous ranges. */
-static int tdb_chainlock_gradual(struct tdb_context *tdb,
-				 size_t off, size_t len)
-{
-	int ret;
-
-	if (len <= 4) {
-		/* Single record.  Just do blocking lock. */
-		return tdb_brlock(tdb, F_WRLCK, off, len, TDB_LOCK_WAIT);
-	}
-
-	/* First we try non-blocking. */
-	ret = tdb_brlock(tdb, F_WRLCK, off, len, TDB_LOCK_NOWAIT);
-	if (ret == 0) {
-		return 0;
-	}
-
-	/* Try locking first half, then second. */
-	ret = tdb_chainlock_gradual(tdb, off, len / 2);
-	if (ret == -1)
-		return -1;
-
-	ret = tdb_chainlock_gradual(tdb, off + len / 2, len - len / 2);
-	if (ret == -1) {
-		tdb_brunlock(tdb, F_WRLCK, off, len / 2);
-		return -1;
-	}
-	return 0;
-}
-
-/* We do the locking gradually to avoid being starved by smaller locks. */
-int tdb_lockall_gradual(struct tdb_context *tdb)
-{
-	int ret;
-
-	/* This checks for other locks, nesting. */
-	ret = tdb_allrecord_check(tdb, F_WRLCK, TDB_LOCK_WAIT, false);
-	if (ret == -1 || ret == 0)
-		return ret;
-
-	/* We cover two kinds of locks:
-	 * 1) Normal chain locks.  Taken for almost all operations.
-	 * 3) Individual records locks.  Taken after normal or free
-	 *    chain locks.
-	 *
-	 * It is (1) which cause the starvation problem, so we're only
-	 * gradual for that. */
-	if (tdb_chainlock_gradual(tdb, FREELIST_TOP,
-				  tdb->header.hash_size * 4) == -1) {
-		return -1;
-	}
-
-	/* Grab individual record locks. */
-	if (tdb_brlock(tdb, F_WRLCK, lock_offset(tdb->header.hash_size), 0,
-		       TDB_LOCK_WAIT) == -1) {
-		tdb_brunlock(tdb, F_WRLCK, FREELIST_TOP,
-			     tdb->header.hash_size * 4);
-		return -1;
-	}
-
-	/* That adds up to an allrecord lock. */
-	tdb->allrecord_lock.count = 1;
-	tdb->allrecord_lock.ltype = F_WRLCK;
-	tdb->allrecord_lock.off = false;
-
-	/* Just check we don't need recovery... */
-	if (tdb_needs_recovery(tdb)) {
-		tdb_allrecord_unlock(tdb, F_WRLCK, false);
-		if (tdb_lock_and_recover(tdb) == -1) {
-			return -1;
-		}
-		/* Try again. */
-		return tdb_lockall_gradual(tdb);
-	}
-
-	return 0;
-}
-
 /* lock/unlock one hash chain. This is meant to be used to reduce
    contention - it cannot guarantee how many records will be locked */
 int tdb_chainlock(struct tdb_context *tdb, TDB_DATA key)

ccan/tdb/tdb.h

@@ -132,7 +132,6 @@ int tdb_lockall_read_nonblock(struct tdb_context *tdb);
 int tdb_unlockall_read(struct tdb_context *tdb);
 int tdb_lockall_mark(struct tdb_context *tdb);
 int tdb_lockall_unmark(struct tdb_context *tdb);
-int tdb_lockall_gradual(struct tdb_context *tdb);
 const char *tdb_name(struct tdb_context *tdb);
 int tdb_fd(struct tdb_context *tdb);
 tdb_log_func tdb_log_fn(struct tdb_context *tdb);

ccan/tdb/tools/starvation.c

@@ -77,9 +77,13 @@ int main(int argc, char *argv[])
 
 	if (strcmp(argv[1], "lockall") == 0)
 		lockall = tdb_lockall;
-	else if (strcmp(argv[1], "gradual") == 0)
+	else if (strcmp(argv[1], "gradual") == 0) {
+#if 0
 		lockall = tdb_lockall_gradual;
-	else
+#else
+		errx(1, "gradual is now the default implementation");
+#endif
+	} else
 		usage("Arg1 should be 'lockall' or 'gradual'");
 
 	num = atoi(argv[2]);