return 0;
}
+static int tdb_lock_and_recover(struct tdb_context *tdb)
+{
+ int ret;
+
+ /* We need to match locking order in transaction commit. */
+ if (tdb_brlock(tdb, F_WRLCK, FREELIST_TOP, 0, TDB_LOCK_WAIT)) {
+ return -1;
+ }
+
+ if (tdb_brlock(tdb, F_WRLCK, OPEN_LOCK, 1, TDB_LOCK_WAIT)) {
+ tdb_brunlock(tdb, F_WRLCK, FREELIST_TOP, 0);
+ return -1;
+ }
+
+ ret = tdb_transaction_recover(tdb);
+
+ tdb_brunlock(tdb, F_WRLCK, OPEN_LOCK, 1);
+ tdb_brunlock(tdb, F_WRLCK, FREELIST_TOP, 0);
+
+ return ret;
+}
+
+static bool have_data_locks(const struct tdb_context *tdb)
+{
+ unsigned int i;
+
+ for (i = 0; i < tdb->num_lockrecs; i++) {
+ if (tdb->lockrecs[i].off >= lock_offset(-1))
+ return true;
+ }
+ return false;
+}
+
static int tdb_lock_list(struct tdb_context *tdb, int list, int ltype,
enum tdb_lock_flags waitflag)
{
int ret;
+ bool check = false;
/* a allrecord lock allows us to avoid per chain locks */
if (tdb->allrecord_lock.count &&
tdb->ecode = TDB_ERR_LOCK;
ret = -1;
} else {
+ /* Only check when we grab first data lock. */
+ check = !have_data_locks(tdb);
ret = tdb_nest_lock(tdb, lock_offset(list), ltype, waitflag);
+
+ if (ret == 0 && check && tdb_needs_recovery(tdb)) {
+ tdb_nest_unlock(tdb, lock_offset(list), ltype, false);
+
+ if (tdb_lock_and_recover(tdb) == -1) {
+ return -1;
+ }
+ return tdb_lock_list(tdb, list, ltype, waitflag);
+ }
}
return ret;
}
return tdb_nest_unlock(tdb, TRANSACTION_LOCK, ltype, false);
}
-
-/* lock/unlock entire database. It can only be upgradable if you have some
- * other way of guaranteeing exclusivity (ie. transaction write lock). */
-int tdb_allrecord_lock(struct tdb_context *tdb, int ltype,
- enum tdb_lock_flags flags, bool upgradable)
+/* Returns 0 if all done, -1 if error, 1 if ok. */
+static int tdb_allrecord_check(struct tdb_context *tdb, int ltype,
+ enum tdb_lock_flags flags, bool upgradable)
{
/* There are no locks on read-only dbs */
if (tdb->read_only || tdb->traverse_read) {
tdb->ecode = TDB_ERR_LOCK;
return -1;
}
+ return 1;
+}
+
+/* lock/unlock entire database. It can only be upgradable if you have some
+ * other way of guaranteeing exclusivity (ie. transaction write lock). */
+int tdb_allrecord_lock(struct tdb_context *tdb, int ltype,
+ enum tdb_lock_flags flags, bool upgradable)
+{
+ switch (tdb_allrecord_check(tdb, ltype, flags, upgradable)) {
+ case -1:
+ return -1;
+ case 0:
+ return 0;
+ }
if (tdb_brlock(tdb, ltype, FREELIST_TOP, 0, flags)) {
if (flags & TDB_LOCK_WAIT) {
tdb->allrecord_lock.ltype = upgradable ? F_WRLCK : ltype;
tdb->allrecord_lock.off = upgradable;
+ if (tdb_needs_recovery(tdb)) {
+ bool mark = flags & TDB_LOCK_MARK_ONLY;
+ tdb_allrecord_unlock(tdb, ltype, mark);
+ if (mark) {
+ tdb->ecode = TDB_ERR_LOCK;
+ TDB_LOG((tdb, TDB_DEBUG_ERROR,
+ "tdb_lockall_mark cannot do recovery\n"));
+ return -1;
+ }
+ if (tdb_lock_and_recover(tdb) == -1) {
+ return -1;
+ }
+ return tdb_allrecord_lock(tdb, ltype, flags, upgradable);
+ }
+
return 0;
}
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)
projects / ccan / blobdiff