+/*
+ * Wait until running transaction passes T_LOCKED state. Also starts the commit
+ * if needed. The function expects running transaction to exist and releases
+ * j_state_lock.
+ */
+static void wait_transaction_locked(journal_t *journal)
+ __releases(journal->j_state_lock)
+{
+ DEFINE_WAIT(wait);
+ int need_to_start;
+ tid_t tid = journal->j_running_transaction->t_tid;
+
+ prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
+ TASK_UNINTERRUPTIBLE);
+ need_to_start = !tid_geq(journal->j_commit_request, tid);
+ read_unlock(&journal->j_state_lock);
+ if (need_to_start)
+ jbd2_log_start_commit(journal, tid);
+ schedule();
+ finish_wait(&journal->j_wait_transaction_locked, &wait);
+}
+
+static void sub_reserved_credits(journal_t *journal, int blocks)
+{
+ atomic_sub(blocks, &journal->j_reserved_credits);
+ wake_up(&journal->j_wait_reserved);
+}
+
+/*
+ * Wait until we can add credits for handle to the running transaction. Called
+ * with j_state_lock held for reading. Returns 0 if handle joined the running
+ * transaction. Returns 1 if we had to wait, j_state_lock is dropped, and
+ * caller must retry.
+ */
+static int add_transaction_credits(journal_t *journal, int blocks,
+ int rsv_blocks)
+{
+ transaction_t *t = journal->j_running_transaction;
+ int needed;
+ int total = blocks + rsv_blocks;
+
+ /*
+ * If the current transaction is locked down for commit, wait
+ * for the lock to be released.
+ */
+ if (t->t_state == T_LOCKED) {
+ wait_transaction_locked(journal);
+ return 1;
+ }
+
+ /*
+ * If there is not enough space left in the log to write all
+ * potential buffers requested by this operation, we need to
+ * stall pending a log checkpoint to free some more log space.
+ */
+ needed = atomic_add_return(total, &t->t_outstanding_credits);
+ if (needed > journal->j_max_transaction_buffers) {
+ /*
+ * If the current transaction is already too large,
+ * then start to commit it: we can then go back and
+ * attach this handle to a new transaction.
+ */
+ atomic_sub(total, &t->t_outstanding_credits);
+ wait_transaction_locked(journal);
+ return 1;
+ }
+
+ /*
+ * The commit code assumes that it can get enough log space
+ * without forcing a checkpoint. This is *critical* for
+ * correctness: a checkpoint of a buffer which is also
+ * associated with a committing transaction creates a deadlock,
+ * so commit simply cannot force through checkpoints.
+ *
+ * We must therefore ensure the necessary space in the journal
+ * *before* starting to dirty potentially checkpointed buffers
+ * in the new transaction.
+ */
+ if (jbd2_log_space_left(journal) < jbd2_space_needed(journal)) {
+ atomic_sub(total, &t->t_outstanding_credits);
+ read_unlock(&journal->j_state_lock);
+ write_lock(&journal->j_state_lock);
+ if (jbd2_log_space_left(journal) < jbd2_space_needed(journal))
+ __jbd2_log_wait_for_space(journal);
+ write_unlock(&journal->j_state_lock);
+ return 1;
+ }
+
+ /* No reservation? We are done... */
+ if (!rsv_blocks)
+ return 0;
+
+ needed = atomic_add_return(rsv_blocks, &journal->j_reserved_credits);
+ /* We allow at most half of a transaction to be reserved */
+ if (needed > journal->j_max_transaction_buffers / 2) {
+ sub_reserved_credits(journal, rsv_blocks);
+ atomic_sub(total, &t->t_outstanding_credits);
+ read_unlock(&journal->j_state_lock);
+ wait_event(journal->j_wait_reserved,
+ atomic_read(&journal->j_reserved_credits) + rsv_blocks
+ <= journal->j_max_transaction_buffers / 2);
+ return 1;
+ }
+ return 0;
+}
+