fix-lockdep-annotation-in-add_transaction_credits

   1 jbd2: fix lockdep annotation in add_transaction_credits()
   2
   3 From: Jan Kara <jack@suse.cz>
   4
   5 Thomas has reported a lockdep splat hitting in
   6 add_transaction_credits(). The problem is that that function calls
   7 jbd2_might_wait_for_commit() while holding j_state_lock which is wrong
   8 (we do not really wait for transaction commit while holding that lock).
   9
  10 Fix the problem by moving jbd2_might_wait_for_commit() into places where
  11 we are ready to wait for transaction commit and thus j_state_lock is
  12 unlocked.
  13
  14 Fixes: 1eaa566d368b214d99cbb973647c1b0b8102a9ae
  15 Reported-by: Thomas Gleixner <tglx@linutronix.de>
  16 Signed-off-by: Jan Kara <jack@suse.cz>
  17 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  18 ---
  19  fs/jbd2/transaction.c | 6 ++++--
  20  1 file changed, 4 insertions(+), 2 deletions(-)
  21
  22 diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
  23 index b5bc3e249163..3d8246a9faa4 100644
  24 --- a/fs/jbd2/transaction.c
  25 +++ b/fs/jbd2/transaction.c
  26 @@ -159,6 +159,7 @@ static void wait_transaction_locked(journal_t *journal)
  27         read_unlock(&journal->j_state_lock);
  28         if (need_to_start)
  29                 jbd2_log_start_commit(journal, tid);
  30 +       jbd2_might_wait_for_commit(journal);
  31         schedule();
  32         finish_wait(&journal->j_wait_transaction_locked, &wait);
  33  }
  34 @@ -182,8 +183,6 @@ static int add_transaction_credits(journal_t *journal, int blocks,
  35         int needed;
  36         int total = blocks + rsv_blocks;
  37
  38 -       jbd2_might_wait_for_commit(journal);
  39 -
  40         /*
  41          * If the current transaction is locked down for commit, wait
  42          * for the lock to be released.
  43 @@ -214,6 +213,7 @@ static int add_transaction_credits(journal_t *journal, int blocks,
  44                 if (atomic_read(&journal->j_reserved_credits) + total >
  45                     journal->j_max_transaction_buffers) {
  46                         read_unlock(&journal->j_state_lock);
  47 +                       jbd2_might_wait_for_commit(journal);
  48                         wait_event(journal->j_wait_reserved,
  49                                    atomic_read(&journal->j_reserved_credits) + total <=
  50                                    journal->j_max_transaction_buffers);
  51 @@ -238,6 +238,7 @@ static int add_transaction_credits(journal_t *journal, int blocks,
  52         if (jbd2_log_space_left(journal) < jbd2_space_needed(journal)) {
  53                 atomic_sub(total, &t->t_outstanding_credits);
  54                 read_unlock(&journal->j_state_lock);
  55 +               jbd2_might_wait_for_commit(journal);
  56                 write_lock(&journal->j_state_lock);
  57                 if (jbd2_log_space_left(journal) < jbd2_space_needed(journal))
  58                         __jbd2_log_wait_for_space(journal);
  59 @@ -255,6 +256,7 @@ static int add_transaction_credits(journal_t *journal, int blocks,
  60                 sub_reserved_credits(journal, rsv_blocks);
  61                 atomic_sub(total, &t->t_outstanding_credits);
  62                 read_unlock(&journal->j_state_lock);
  63 +               jbd2_might_wait_for_commit(journal);
  64                 wait_event(journal->j_wait_reserved,
  65                          atomic_read(&journal->j_reserved_credits) + rsv_blocks
  66                          <= journal->j_max_transaction_buffers / 2);
  67 --
  68 2.6.6
  69
  70