jbd2: Fix assertion failure in fs/jbd2/checkpoint.c
Before we start committing a transaction, we call __journal_clean_checkpoint_list() to cleanup transaction's written-back buffers. If this call happens to remove all of them (and there were already some buffers), __journal_remove_checkpoint() will decide to free the transaction because it isn't (yet) a committing transaction and soon we fail some assertion - the transaction really isn't ready to be freed :). We change the check in __journal_remove_checkpoint() to free only a transaction in T_FINISHED state. The locking there is subtle though (as everywhere in JBD ;(). We use j_list_lock to protect the check and a subsequent call to __journal_drop_transaction() and do the same in the end of journal_commit_transaction() which is the only place where a transaction can get to T_FINISHED state. Probably I'm too paranoid here and such locking is not really necessary - checkpoint lists are processed only from log_do_checkpoint() where a transaction must be already committed to be processed or from __journal_clean_checkpoint_list() where kjournald itself calls it and thus transaction cannot change state either. Better be safe if something changes in future... Signed-off-by: Jan Kara <jack@suse.cz> Cc: <linux-ext4@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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@ -602,15 +602,15 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
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/*
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* There is one special case to worry about: if we have just pulled the
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* buffer off a committing transaction's forget list, then even if the
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* checkpoint list is empty, the transaction obviously cannot be
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* dropped!
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* buffer off a running or committing transaction's checkpoing list,
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* then even if the checkpoint list is empty, the transaction obviously
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* cannot be dropped!
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*
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* The locking here around j_committing_transaction is a bit sleazy.
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* The locking here around t_state is a bit sleazy.
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* See the comment at the end of jbd2_journal_commit_transaction().
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*/
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if (transaction == journal->j_committing_transaction) {
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JBUFFER_TRACE(jh, "belongs to committing transaction");
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if (transaction->t_state != T_FINISHED) {
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JBUFFER_TRACE(jh, "belongs to running/committing transaction");
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goto out;
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}
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@ -867,10 +867,10 @@ restart_loop:
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}
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spin_unlock(&journal->j_list_lock);
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/*
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* This is a bit sleazy. We borrow j_list_lock to protect
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* journal->j_committing_transaction in __jbd2_journal_remove_checkpoint.
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* Really, __jbd2_journal_remove_checkpoint should be using j_state_lock but
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* it's a bit hassle to hold that across __jbd2_journal_remove_checkpoint
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* This is a bit sleazy. We use j_list_lock to protect transition
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* of a transaction into T_FINISHED state and calling
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* __jbd2_journal_drop_transaction(). Otherwise we could race with
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* other checkpointing code processing the transaction...
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*/
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spin_lock(&journal->j_state_lock);
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spin_lock(&journal->j_list_lock);
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@ -442,6 +442,8 @@ struct transaction_s
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/*
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* Transaction's current state
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* [no locking - only kjournald2 alters this]
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* [j_list_lock] guards transition of a transaction into T_FINISHED
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* state and subsequent call of __jbd2_journal_drop_transaction()
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* FIXME: needs barriers
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* KLUDGE: [use j_state_lock]
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*/
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