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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/transaction.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/transaction.c')
-rw-r--r--fs/jbd/transaction.c73
1 files changed, 37 insertions, 36 deletions
diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c
index dc39efd05d5..7e59c6e66f9 100644
--- a/fs/jbd/transaction.c
+++ b/fs/jbd/transaction.c
@@ -696,7 +696,6 @@ repeat:
if (!jh->b_transaction) {
JBUFFER_TRACE(jh, "no transaction");
J_ASSERT_JH(jh, !jh->b_next_transaction);
- jh->b_transaction = transaction;
JBUFFER_TRACE(jh, "file as BJ_Reserved");
spin_lock(&journal->j_list_lock);
__journal_file_buffer(jh, transaction, BJ_Reserved);
@@ -818,7 +817,6 @@ int journal_get_create_access(handle_t *handle, struct buffer_head *bh)
* committed and so it's safe to clear the dirty bit.
*/
clear_buffer_dirty(jh2bh(jh));
- jh->b_transaction = transaction;
/* first access by this transaction */
jh->b_modified = 0;
@@ -1069,8 +1067,9 @@ int journal_dirty_data(handle_t *handle, struct buffer_head *bh)
ret = -EIO;
goto no_journal;
}
-
- if (jh->b_transaction != NULL) {
+ /* We might have slept so buffer could be refiled now */
+ if (jh->b_transaction != NULL &&
+ jh->b_transaction != handle->h_transaction) {
JBUFFER_TRACE(jh, "unfile from commit");
__journal_temp_unlink_buffer(jh);
/* It still points to the committing
@@ -1091,8 +1090,6 @@ int journal_dirty_data(handle_t *handle, struct buffer_head *bh)
if (jh->b_jlist != BJ_SyncData && jh->b_jlist != BJ_Locked) {
JBUFFER_TRACE(jh, "not on correct data list: unfile");
J_ASSERT_JH(jh, jh->b_jlist != BJ_Shadow);
- __journal_temp_unlink_buffer(jh);
- jh->b_transaction = handle->h_transaction;
JBUFFER_TRACE(jh, "file as data");
__journal_file_buffer(jh, handle->h_transaction,
BJ_SyncData);
@@ -1300,8 +1297,6 @@ int journal_forget (handle_t *handle, struct buffer_head *bh)
__journal_file_buffer(jh, transaction, BJ_Forget);
} else {
__journal_unfile_buffer(jh);
- journal_remove_journal_head(bh);
- __brelse(bh);
if (!buffer_jbd(bh)) {
spin_unlock(&journal->j_list_lock);
jbd_unlock_bh_state(bh);
@@ -1622,19 +1617,32 @@ static void __journal_temp_unlink_buffer(struct journal_head *jh)
mark_buffer_dirty(bh); /* Expose it to the VM */
}
+/*
+ * Remove buffer from all transactions.
+ *
+ * Called with bh_state lock and j_list_lock
+ *
+ * jh and bh may be already freed when this function returns.
+ */
void __journal_unfile_buffer(struct journal_head *jh)
{
__journal_temp_unlink_buffer(jh);
jh->b_transaction = NULL;
+ journal_put_journal_head(jh);
}
void journal_unfile_buffer(journal_t *journal, struct journal_head *jh)
{
- jbd_lock_bh_state(jh2bh(jh));
+ struct buffer_head *bh = jh2bh(jh);
+
+ /* Get reference so that buffer cannot be freed before we unlock it */
+ get_bh(bh);
+ jbd_lock_bh_state(bh);
spin_lock(&journal->j_list_lock);
__journal_unfile_buffer(jh);
spin_unlock(&journal->j_list_lock);
- jbd_unlock_bh_state(jh2bh(jh));
+ jbd_unlock_bh_state(bh);
+ __brelse(bh);
}
/*
@@ -1661,16 +1669,12 @@ __journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh)
/* A written-back ordered data buffer */
JBUFFER_TRACE(jh, "release data");
__journal_unfile_buffer(jh);
- journal_remove_journal_head(bh);
- __brelse(bh);
}
} else if (jh->b_cp_transaction != NULL && jh->b_transaction == NULL) {
/* written-back checkpointed metadata buffer */
if (jh->b_jlist == BJ_None) {
JBUFFER_TRACE(jh, "remove from checkpoint list");
__journal_remove_checkpoint(jh);
- journal_remove_journal_head(bh);
- __brelse(bh);
}
}
spin_unlock(&journal->j_list_lock);
@@ -1733,7 +1737,7 @@ int journal_try_to_free_buffers(journal_t *journal,
/*
* We take our own ref against the journal_head here to avoid
* having to add tons of locking around each instance of
- * journal_remove_journal_head() and journal_put_journal_head().
+ * journal_put_journal_head().
*/
jh = journal_grab_journal_head(bh);
if (!jh)
@@ -1770,10 +1774,9 @@ static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
int may_free = 1;
struct buffer_head *bh = jh2bh(jh);
- __journal_unfile_buffer(jh);
-
if (jh->b_cp_transaction) {
JBUFFER_TRACE(jh, "on running+cp transaction");
+ __journal_temp_unlink_buffer(jh);
/*
* We don't want to write the buffer anymore, clear the
* bit so that we don't confuse checks in
@@ -1784,8 +1787,7 @@ static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
may_free = 0;
} else {
JBUFFER_TRACE(jh, "on running transaction");
- journal_remove_journal_head(bh);
- __brelse(bh);
+ __journal_unfile_buffer(jh);
}
return may_free;
}
@@ -2070,6 +2072,8 @@ void __journal_file_buffer(struct journal_head *jh,
if (jh->b_transaction)
__journal_temp_unlink_buffer(jh);
+ else
+ journal_grab_journal_head(bh);
jh->b_transaction = transaction;
switch (jlist) {
@@ -2127,9 +2131,10 @@ void journal_file_buffer(struct journal_head *jh,
* already started to be used by a subsequent transaction, refile the
* buffer on that transaction's metadata list.
*
- * Called under journal->j_list_lock
- *
+ * Called under j_list_lock
* Called under jbd_lock_bh_state(jh2bh(jh))
+ *
+ * jh and bh may be already free when this function returns
*/
void __journal_refile_buffer(struct journal_head *jh)
{
@@ -2153,6 +2158,11 @@ void __journal_refile_buffer(struct journal_head *jh)
was_dirty = test_clear_buffer_jbddirty(bh);
__journal_temp_unlink_buffer(jh);
+ /*
+ * We set b_transaction here because b_next_transaction will inherit
+ * our jh reference and thus __journal_file_buffer() must not take a
+ * new one.
+ */
jh->b_transaction = jh->b_next_transaction;
jh->b_next_transaction = NULL;
if (buffer_freed(bh))
@@ -2169,30 +2179,21 @@ void __journal_refile_buffer(struct journal_head *jh)
}
/*
- * For the unlocked version of this call, also make sure that any
- * hanging journal_head is cleaned up if necessary.
- *
- * __journal_refile_buffer is usually called as part of a single locked
- * operation on a buffer_head, in which the caller is probably going to
- * be hooking the journal_head onto other lists. In that case it is up
- * to the caller to remove the journal_head if necessary. For the
- * unlocked journal_refile_buffer call, the caller isn't going to be
- * doing anything else to the buffer so we need to do the cleanup
- * ourselves to avoid a jh leak.
- *
- * *** The journal_head may be freed by this call! ***
+ * __journal_refile_buffer() with necessary locking added. We take our bh
+ * reference so that we can safely unlock bh.
+ *
+ * The jh and bh may be freed by this call.
*/
void journal_refile_buffer(journal_t *journal, struct journal_head *jh)
{
struct buffer_head *bh = jh2bh(jh);
+ /* Get reference so that buffer cannot be freed before we unlock it */
+ get_bh(bh);
jbd_lock_bh_state(bh);
spin_lock(&journal->j_list_lock);
-
__journal_refile_buffer(jh);
jbd_unlock_bh_state(bh);
- journal_remove_journal_head(bh);
-
spin_unlock(&journal->j_list_lock);
__brelse(bh);
}