From bb189247f35688a3353545902c56290fb7d7754a Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Fri, 24 Jun 2011 23:11:59 +0200 Subject: jbd: Fix oops in journal_remove_journal_head() 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 journal_commit_transaction() ... processing t_forget list __journal_refile_buffer(jh); if (!jh->b_transaction) { jbd_unlock_bh_state(bh); journal_try_to_free_buffers() journal_grab_journal_head(bh) jbd_lock_bh_state(bh) __journal_try_to_free_buffer() journal_put_journal_head(jh) journal_remove_journal_head(bh); 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 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 journal_remove_journal_head() and instead just remove journal_head when b_jcount drops to zero. The result of this is that [__]journal_refile_buffer(), [__]journal_unfile_buffer(), and __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 --- include/linux/jbd.h | 1 - 1 file changed, 1 deletion(-) (limited to 'include/linux/jbd.h') diff --git a/include/linux/jbd.h b/include/linux/jbd.h index e069650..e6a5e34 100644 --- a/include/linux/jbd.h +++ b/include/linux/jbd.h @@ -940,7 +940,6 @@ extern int journal_force_commit(journal_t *); */ struct journal_head *journal_add_journal_head(struct buffer_head *bh); struct journal_head *journal_grab_journal_head(struct buffer_head *bh); -void journal_remove_journal_head(struct buffer_head *bh); void journal_put_journal_head(struct journal_head *jh); /* -- cgit v1.1