linux-sg2042/fs/jbd2
Jan Kara de1b794130 jbd2: Fix oops in jbd2_journal_remove_journal_head()
jbd2_journal_remove_journal_head() can oops when trying to access
journal_head returned by bh2jh(). This is caused for example by the
following race:

	TASK1					TASK2
  jbd2_journal_commit_transaction()
    ...
    processing t_forget list
      __jbd2_journal_refile_buffer(jh);
      if (!jh->b_transaction) {
        jbd_unlock_bh_state(bh);
					jbd2_journal_try_to_free_buffers()
					  jbd2_journal_grab_journal_head(bh)
					  jbd_lock_bh_state(bh)
					  __journal_try_to_free_buffer()
					  jbd2_journal_put_journal_head(jh)
        jbd2_journal_remove_journal_head(bh);

jbd2_journal_put_journal_head() in TASK2 sees that b_jcount == 0 and
buffer is not part of any transaction and thus frees journal_head
before TASK1 gets to doing so. Note that even buffer_head can be
released by try_to_free_buffers() after
jbd2_journal_put_journal_head() which adds even larger opportunity for
oops (but I didn't see this happen in reality).

Fix the problem by making transactions hold their own journal_head
reference (in b_jcount). That way we don't have to remove journal_head
explicitely via jbd2_journal_remove_journal_head() and instead just
remove journal_head when b_jcount drops to zero. The result of this is
that [__]jbd2_journal_refile_buffer(),
[__]jbd2_journal_unfile_buffer(), and
__jdb2_journal_remove_checkpoint() can free journal_head which needs
modification of a few callers. Also we have to be careful because once
journal_head is removed, buffer_head might be freed as well. So we
have to get our own buffer_head reference where it matters.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2011-06-13 15:38:22 -04:00
..
Kconfig Revert "task_struct: make journal_info conditional" 2009-12-17 13:23:24 -08:00
Makefile [PATCH] jbd2: rename jbd2 symbols to avoid duplication of jbd symbols 2006-10-11 11:14:15 -07:00
checkpoint.c jbd2: Fix oops in jbd2_journal_remove_journal_head() 2011-06-13 15:38:22 -04:00
commit.c jbd2: Fix oops in jbd2_journal_remove_journal_head() 2011-06-13 15:38:22 -04:00
journal.c jbd2: Fix oops in jbd2_journal_remove_journal_head() 2011-06-13 15:38:22 -04:00
recovery.c jbd2: move debug message into debug #ifdef 2010-12-18 13:36:33 -05:00
revoke.c Fix common misspellings 2011-03-31 11:26:23 -03:00
transaction.c jbd2: Fix oops in jbd2_journal_remove_journal_head() 2011-06-13 15:38:22 -04:00