jbd2-fix-lockdep-splat-with-generic-270

   1 jbd2: Fix lockdep splat with generic/270 test
   2
   3 From: Jan Kara <jack@suse.cz>
   4
   5 I've hit a lockdep splat with generic/270 test complaining that:
   6
   7 3216.fsstress.b/3533 is trying to acquire lock:
   8  (jbd2_handle){++++..}, at: [<ffffffff813152e0>] jbd2_log_wait_commit+0x0/0x150
   9
  10 but task is already holding lock:
  11  (jbd2_handle){++++..}, at: [<ffffffff8130bd3b>] start_this_handle+0x35b/0x850
  12
  13 The underlying problem is that jbd2_journal_force_commit_nested()
  14 (called from ext4_should_retry_alloc()) may get called while a
  15 transaction handle is started. In such case it takes care to not wait
  16 for commit of the running transaction (which would deadlock) but only
  17 for a commit of a transaction that is already committing (which is safe
  18 as that doesn't wait for any filesystem locks).
  19
  20 In fact there are also other callers of jbd2_log_wait_commit() that take
  21 care to pass tid of a transaction that is already committing and for
  22 those cases, the lockdep instrumentation is too restrictive and leading
  23 to false positive reports. Fix the problem by calling
  24 jbd2_might_wait_for_commit() from jbd2_log_wait_commit() only if the
  25 transaction isn't already committing.
  26
  27 Fixes: 1eaa566d368b214d99cbb973647c1b0b8102a9ae
  28 Signed-off-by: Jan Kara <jack@suse.cz>
  29 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  30 ---
  31  fs/jbd2/journal.c | 15 ++++++++++++++-
  32  1 file changed, 14 insertions(+), 1 deletion(-)
  33
  34 diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
  35 index 5adc2fb62b0f..9410ec462ba6 100644
  36 --- a/fs/jbd2/journal.c
  37 +++ b/fs/jbd2/journal.c
  38 @@ -691,8 +691,21 @@ int jbd2_log_wait_commit(journal_t *journal, tid_t tid)
  39  {
  40         int err = 0;
  41
  42 -       jbd2_might_wait_for_commit(journal);
  43         read_lock(&journal->j_state_lock);
  44 +#ifdef CONFIG_PROVE_LOCKING
  45 +       /*
  46 +        * Some callers make sure transaction is already committing and in that
  47 +        * case we cannot block on open handles anymore. So don't warn in that
  48 +        * case.
  49 +        */
  50 +       if (tid_gt(tid, journal->j_commit_sequence) &&
  51 +           (!journal->j_committing_transaction ||
  52 +            journal->j_committing_transaction->t_tid != tid)) {
  53 +               read_unlock(&journal->j_state_lock);
  54 +               jbd2_might_wait_for_commit(journal);
  55 +               read_lock(&journal->j_state_lock);
  56 +       }
  57 +#endif
  58  #ifdef CONFIG_JBD2_DEBUG
  59         if (!tid_geq(journal->j_commit_request, tid)) {
  60                 printk(KERN_ERR
  61 --
  62 2.12.0
  63
  64