ext4: allow an active handle to be started when freezing
authorYongqiang Yang <xiaoqiangnk@gmail.com>
Mon, 11 Apr 2011 02:06:07 +0000 (22:06 -0400)
committerTheodore Ts'o <tytso@mit.edu>
Mon, 11 Apr 2011 02:06:07 +0000 (22:06 -0400)
commitbe4f27d324e8ddd57cc0d4d604fe85ee0425cba9
treee4262a9e1ade9095e1bf937dc4b9d56a08824eda
parent0893ed458b4b1d7c7667ca7ffb8b11febe7e7e6c
ext4: allow an active handle to be started when freezing

ext4_journal_start_sb() should not prevent an active handle from being
started due to s_frozen.  Otherwise, deadlock is easy to happen, below
is a situation.

================================================
     freeze         |       truncate
================================================
                    |  ext4_ext_truncate()
    freeze_super()  |   starts a handle
    sets s_frozen   |
                    |  ext4_ext_truncate()
                    |  holds i_data_sem
  ext4_freeze()     |
  waits for updates |
                    |  ext4_free_blocks()
                    |  calls dquot_free_block()
                    |
                    |  dquot_free_blocks()
                    |  calls ext4_dirty_inode()
                    |
                    |  ext4_dirty_inode()
                    |  trys to start an active
                    |  handle
                    |
                    |  block due to s_frozen
================================================

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reported-by: Amir Goldstein <amir73il@users.sf.net>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
fs/ext4/super.c