do-not-descrease-bufferheads-refcount

   1 jbd2: flush_descriptor(): Do not decrease buffer head's ref count
   2
   3 From: Chandan Rajendra <chandan@linux.ibm.com>
   4
   5 When executing generic/388 on a ppc64le machine, we notice the following
   6 call trace,
   7
   8 VFS: brelse: Trying to free free buffer
   9 WARNING: CPU: 0 PID: 6637 at /root/repos/linux/fs/buffer.c:1195 __brelse+0x84/0xc0
  10
  11 Call Trace:
  12  __brelse+0x80/0xc0 (unreliable)
  13  invalidate_bh_lru+0x78/0xc0
  14  on_each_cpu_mask+0xa8/0x130
  15  on_each_cpu_cond_mask+0x130/0x170
  16  invalidate_bh_lrus+0x44/0x60
  17  invalidate_bdev+0x38/0x70
  18  ext4_put_super+0x294/0x560
  19  generic_shutdown_super+0xb0/0x170
  20  kill_block_super+0x38/0xb0
  21  deactivate_locked_super+0xa4/0xf0
  22  cleanup_mnt+0x164/0x1d0
  23  task_work_run+0x110/0x160
  24  do_notify_resume+0x414/0x460
  25  ret_from_except_lite+0x70/0x74
  26
  27 The warning happens because flush_descriptor() drops bh reference it
  28 does not own. The bh reference acquired by
  29 jbd2_journal_get_descriptor_buffer() is owned by the log_bufs list and
  30 gets released when this list is processed. The reference for doing IO is
  31 only acquired in write_dirty_buffer() later in flush_descriptor().
  32
  33 Reported-by: Harish Sriram <harish@linux.ibm.com>
  34 Reviewed-by: Jan Kara <jack@suse.cz>
  35 Signed-off-by: Chandan Rajendra <chandan@linux.ibm.com>
  36 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  37 ---
  38 Changelog:
  39 V1 -> V2:
  40 1. Fix commit message.
  41
  42  fs/jbd2/revoke.c | 4 +---
  43  1 file changed, 1 insertion(+), 3 deletions(-)
  44
  45 diff --git a/fs/jbd2/revoke.c b/fs/jbd2/revoke.c
  46 index 69b9bc329964..f08073d7bbf5 100644
  47 --- a/fs/jbd2/revoke.c
  48 +++ b/fs/jbd2/revoke.c
  49 @@ -638,10 +638,8 @@ static void flush_descriptor(journal_t *journal,
  50  {
  51         jbd2_journal_revoke_header_t *header;
  52
  53 -       if (is_journal_aborted(journal)) {
  54 -               put_bh(descriptor);
  55 +       if (is_journal_aborted(journal))
  56                 return;
  57 -       }
  58
  59         header = (jbd2_journal_revoke_header_t *)descriptor->b_data;
  60         header->r_count = cpu_to_be32(offset);
  61 --
  62 2.19.1
  63
  64