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Date: Mon, 21 Jan 2008 22:02:05 -0500 From: "Theodore Ts'o" <tytso@....EDU> To: linux-kernel@...r.kernel.org Cc: Jan Kara <jack@...e.cz>, <linux-ext4@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: [PATCH 26/49] jbd2: Fix assertion failure in fs/jbd2/checkpoint.c From: Jan Kara <jack@...e.cz> 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@...e.cz> Cc: <linux-ext4@...r.kernel.org> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org> --- fs/jbd2/checkpoint.c | 12 ++++++------ fs/jbd2/commit.c | 8 ++++---- include/linux/jbd2.h | 2 ++ 3 files changed, 12 insertions(+), 10 deletions(-) diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c index 3fccde7..7e958c8 100644 --- a/fs/jbd2/checkpoint.c +++ b/fs/jbd2/checkpoint.c @@ -602,15 +602,15 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh) /* * There is one special case to worry about: if we have just pulled the - * buffer off a committing transaction's forget list, then even if the - * checkpoint list is empty, the transaction obviously cannot be - * dropped! + * buffer off a running or committing transaction's checkpoing list, + * then even if the checkpoint list is empty, the transaction obviously + * cannot be dropped! * - * The locking here around j_committing_transaction is a bit sleazy. + * The locking here around t_state is a bit sleazy. * See the comment at the end of jbd2_journal_commit_transaction(). */ - if (transaction == journal->j_committing_transaction) { - JBUFFER_TRACE(jh, "belongs to committing transaction"); + if (transaction->t_state != T_FINISHED) { + JBUFFER_TRACE(jh, "belongs to running/committing transaction"); goto out; } diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c index 6986f33..39b5cee 100644 --- a/fs/jbd2/commit.c +++ b/fs/jbd2/commit.c @@ -867,10 +867,10 @@ restart_loop: } spin_unlock(&journal->j_list_lock); /* - * This is a bit sleazy. We borrow j_list_lock to protect - * journal->j_committing_transaction in __jbd2_journal_remove_checkpoint. - * Really, __jbd2_journal_remove_checkpoint should be using j_state_lock but - * it's a bit hassle to hold that across __jbd2_journal_remove_checkpoint + * This is a bit sleazy. We use j_list_lock to protect transition + * of a transaction into T_FINISHED state and calling + * __jbd2_journal_drop_transaction(). Otherwise we could race with + * other checkpointing code processing the transaction... */ spin_lock(&journal->j_state_lock); spin_lock(&journal->j_list_lock); diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h index d5f7cff..d861ffd 100644 --- a/include/linux/jbd2.h +++ b/include/linux/jbd2.h @@ -442,6 +442,8 @@ struct transaction_s /* * Transaction's current state * [no locking - only kjournald2 alters this] + * [j_list_lock] guards transition of a transaction into T_FINISHED + * state and subsequent call of __jbd2_journal_drop_transaction() * FIXME: needs barriers * KLUDGE: [use j_state_lock] */ -- 1.5.4.rc3.31.g1271-dirty - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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