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authorJan Kara <jack@suse.cz>2011-06-24 23:11:59 +0200
committerJan Kara <jack@suse.cz>2011-06-27 11:44:37 +0200
commitbb189247f35688a3353545902c56290fb7d7754a (patch)
tree02f93da7f642f3e59050d1c2837a7a8a8e61b3aa /fs/jbd/checkpoint.c
parent2c2ea9451fc2a12ee57c8346f0da26969d07ee7f (diff)
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 <jack@suse.cz>
Diffstat (limited to 'fs/jbd/checkpoint.c')
-rw-r--r--fs/jbd/checkpoint.c27
1 files changed, 15 insertions, 12 deletions
diff --git a/fs/jbd/checkpoint.c b/fs/jbd/checkpoint.c
index dea7503b47e..61655a37c73 100644
--- a/fs/jbd/checkpoint.c
+++ b/fs/jbd/checkpoint.c
@@ -96,10 +96,14 @@ static int __try_to_free_cp_buf(struct journal_head *jh)
if (jh->b_jlist == BJ_None && !buffer_locked(bh) &&
!buffer_dirty(bh) && !buffer_write_io_error(bh)) {
+ /*
+ * Get our reference so that bh cannot be freed before
+ * we unlock it
+ */
+ get_bh(bh);
JBUFFER_TRACE(jh, "remove from checkpoint list");
ret = __journal_remove_checkpoint(jh) + 1;
jbd_unlock_bh_state(bh);
- journal_remove_journal_head(bh);
BUFFER_TRACE(bh, "release");
__brelse(bh);
} else {
@@ -221,8 +225,8 @@ restart:
spin_lock(&journal->j_list_lock);
goto restart;
}
+ get_bh(bh);
if (buffer_locked(bh)) {
- get_bh(bh);
spin_unlock(&journal->j_list_lock);
jbd_unlock_bh_state(bh);
wait_on_buffer(bh);
@@ -241,7 +245,6 @@ restart:
*/
released = __journal_remove_checkpoint(jh);
jbd_unlock_bh_state(bh);
- journal_remove_journal_head(bh);
__brelse(bh);
}
@@ -305,12 +308,12 @@ static int __process_buffer(journal_t *journal, struct journal_head *jh,
ret = 1;
if (unlikely(buffer_write_io_error(bh)))
ret = -EIO;
+ get_bh(bh);
J_ASSERT_JH(jh, !buffer_jbddirty(bh));
BUFFER_TRACE(bh, "remove from checkpoint");
__journal_remove_checkpoint(jh);
spin_unlock(&journal->j_list_lock);
jbd_unlock_bh_state(bh);
- journal_remove_journal_head(bh);
__brelse(bh);
} else {
/*
@@ -526,9 +529,9 @@ int cleanup_journal_tail(journal_t *journal)
/*
* journal_clean_one_cp_list
*
- * Find all the written-back checkpoint buffers in the given list and release them.
+ * Find all the written-back checkpoint buffers in the given list and release
+ * them.
*
- * Called with the journal locked.
* Called with j_list_lock held.
* Returns number of bufers reaped (for debug)
*/
@@ -635,8 +638,8 @@ out:
* checkpoint lists.
*
* The function returns 1 if it frees the transaction, 0 otherwise.
+ * The function can free jh and bh.
*
- * This function is called with the journal locked.
* This function is called with j_list_lock held.
* This function is called with jbd_lock_bh_state(jh2bh(jh))
*/
@@ -655,13 +658,14 @@ int __journal_remove_checkpoint(struct journal_head *jh)
}
journal = transaction->t_journal;
+ JBUFFER_TRACE(jh, "removing from transaction");
__buffer_unlink(jh);
jh->b_cp_transaction = NULL;
+ journal_put_journal_head(jh);
if (transaction->t_checkpoint_list != NULL ||
transaction->t_checkpoint_io_list != NULL)
goto out;
- JBUFFER_TRACE(jh, "transaction has no more buffers");
/*
* There is one special case to worry about: if we have just pulled the
@@ -672,10 +676,8 @@ int __journal_remove_checkpoint(struct journal_head *jh)
* The locking here around t_state is a bit sleazy.
* See the comment at the end of journal_commit_transaction().
*/
- if (transaction->t_state != T_FINISHED) {
- JBUFFER_TRACE(jh, "belongs to running/committing transaction");
+ if (transaction->t_state != T_FINISHED)
goto out;
- }
/* OK, that was the last buffer for the transaction: we can now
safely remove this transaction from the log */
@@ -687,7 +689,6 @@ int __journal_remove_checkpoint(struct journal_head *jh)
wake_up(&journal->j_wait_logspace);
ret = 1;
out:
- JBUFFER_TRACE(jh, "exit");
return ret;
}
@@ -706,6 +707,8 @@ void __journal_insert_checkpoint(struct journal_head *jh,
J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
+ /* Get reference for checkpointing transaction */
+ journal_grab_journal_head(jh2bh(jh));
jh->b_cp_transaction = transaction;
if (!transaction->t_checkpoint_list) {