jbd2: call __jbd2_log_start_commit with j_state_lock write locked

On an SMP ARM system running ext4, I've received a report that the
first J_ASSERT in jbd2_journal_commit_transaction has been triggering:

	J_ASSERT(journal->j_running_transaction != NULL);

While investigating possible causes for this problem, I noticed that
__jbd2_log_start_commit() is getting called with j_state_lock only
read-locked, in spite of the fact that it's possible for it might
j_commit_request.  Fix this by grabbing the necessary information so
we can test to see if we need to start a new transaction before
dropping the read lock, and then calling jbd2_log_start_commit() which
will grab the write lock.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 7 insertions, 2 deletions

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 9e4686900f18..97e73469b2c4 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -473,7 +473,8 @@ int __jbd2_log_space_left(journal_t *journal)
 }
 
 /*
- * Called under j_state_lock.  Returns true if a transaction commit was started.
+ * Called with j_state_lock locked for writing.
+ * Returns true if a transaction commit was started.
  */
 int __jbd2_log_start_commit(journal_t *journal, tid_t target)
 {
@@ -520,11 +521,13 @@ int jbd2_journal_force_commit_nested(journal_t *journal)
 {
         transaction_t *transaction = NULL;
         tid_t tid;
+        int need_to_start = 0;
 
         read_lock(&journal->j_state_lock);
         if (journal->j_running_transaction && !current->journal_info) {
                 transaction = journal->j_running_transaction;
-                __jbd2_log_start_commit(journal, transaction->t_tid);
+                if (!tid_geq(journal->j_commit_request, transaction->t_tid))
+                        need_to_start = 1;
         } else if (journal->j_committing_transaction)
                 transaction = journal->j_committing_transaction;
 
@@ -535,6 +538,8 @@ int jbd2_journal_force_commit_nested(journal_t *journal)
 
         tid = transaction->t_tid;
         read_unlock(&journal->j_state_lock);
+        if (need_to_start)
+                jbd2_log_start_commit(journal, tid);
         jbd2_log_wait_commit(journal, tid);
         return 1;
 }