dont-elevate-b_count-before-calling-__jbd2_journal_remove_checkpoint

   1 jbd2: don't call get_bh() before calling __jbd2_journal_remove_checkpoint()
   2
   3 The __jbd2_journal_remove_checkpoint() doesn't require an elevated
   4 b_count; indeed, until the jh structure gets released by the call to
   5 jbd2_journal_put_journal_head(), the bh's b_count is elevated by
   6 virtue of the existence of the jh structure.
   7
   8 Suggested-by: Jan Kara <jack@suse.cz>
   9 Reviewed-by: Jan Kara <jack@suse.cz>
  10 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  11 ---
  12  fs/jbd2/checkpoint.c | 19 +++++--------------
  13  1 file changed, 5 insertions(+), 14 deletions(-)
  14
  15 diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
  16 index 18c7a8d..90d6091 100644
  17 --- a/fs/jbd2/checkpoint.c
  18 +++ b/fs/jbd2/checkpoint.c
  19 @@ -96,15 +96,8 @@ static int __try_to_free_cp_buf(struct journal_head *jh)
  20
  21         if (jh->b_transaction == NULL && !buffer_locked(bh) &&
  22             !buffer_dirty(bh) && !buffer_write_io_error(bh)) {
  23 -               /*
  24 -                * Get our reference so that bh cannot be freed before
  25 -                * we unlock it
  26 -                */
  27 -               get_bh(bh);
  28                 JBUFFER_TRACE(jh, "remove from checkpoint list");
  29                 ret = __jbd2_journal_remove_checkpoint(jh) + 1;
  30 -               BUFFER_TRACE(bh, "release");
  31 -               __brelse(bh);
  32         }
  33         return ret;
  34  }
  35 @@ -216,7 +209,7 @@ int jbd2_log_do_checkpoint(journal_t *journal)
  36         struct buffer_head      *bh;
  37         transaction_t           *transaction;
  38         tid_t                   this_tid;
  39 -       int                     result, batch_count = 0, done = 0;
  40 +       int                     result, batch_count = 0;
  41
  42         jbd_debug(1, "Start checkpoint\n");
  43
  44 @@ -291,11 +284,9 @@ restart:
  45                 if (!buffer_dirty(bh)) {
  46                         if (unlikely(buffer_write_io_error(bh)) && !result)
  47                                 result = -EIO;
  48 -                       get_bh(bh);
  49                         BUFFER_TRACE(bh, "remove from checkpoint");
  50                         __jbd2_journal_remove_checkpoint(jh);
  51                         spin_unlock(&journal->j_list_lock);
  52 -                       __brelse(bh);
  53                         goto retry;
  54                 }
  55                 /*
  56 @@ -338,12 +329,12 @@ restart2:
  57             transaction->t_tid != this_tid)
  58                 goto out;
  59
  60 -       while (!done && transaction->t_checkpoint_io_list) {
  61 +       while (transaction->t_checkpoint_io_list) {
  62                 jh = transaction->t_checkpoint_io_list;
  63                 bh = jh2bh(jh);
  64 -               get_bh(bh);
  65                 if (buffer_locked(bh)) {
  66                         spin_unlock(&journal->j_list_lock);
  67 +                       get_bh(bh);
  68                         wait_on_buffer(bh);
  69                         /* the journal_head may have gone by now */
  70                         BUFFER_TRACE(bh, "brelse");
  71 @@ -359,8 +350,8 @@ restart2:
  72                  * know that it has been written out and so we can
  73                  * drop it from the list
  74                  */
  75 -               done = __jbd2_journal_remove_checkpoint(jh);
  76 -               __brelse(bh);
  77 +               if (__jbd2_journal_remove_checkpoint(jh))
  78 +                       break;
  79         }
  80  out:
  81         spin_unlock(&journal->j_list_lock);