linux-ext4 - Understanding ext3

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Date:	Sat, 11 Nov 2006 16:45:52 +0530
From:	"Ratna Manoj" <manoj.br@...il.com>
To:	linux-ext4@...r.kernel.org
Cc:	sct@...hat.com
Subject: Understanding ext3

---------- Forwarded message ----------
From: Ratna Manoj <manoj.br@...il.com>
Date: Nov 11, 2006 4:35 PM
Subject: sct@...hat.com
To: linux-ext4@...r.kernel.org


Hi,


int journal_dirty_data(handle_t *handle, struct buffer_head *bh)
{
                        ..................
                        ..................

                         /*
                         * This buffer may be undergoing writeout in commit.  We
                         * can't return from here and let the caller dirty it
                         * again because that can cause the write-out loop in
                         * commit to never terminate.
                         */
                         if (buffer_dirty(bh)) {
                                 get_bh(bh);
                                 spin_unlock(&journal->j_list_lock);
                                 jbd_unlock_bh_state(bh);
                                 need_brelse = 1;
                                 sync_dirty_buffer(bh);
                                 jbd_lock_bh_state(bh);
                                 spin_lock(&journal->j_list_lock);
                                 /* The buffer may become locked again at any
                                    time if it is redirtied */
                         }
                         ..............................
                         ..............................
}


Can any body please explain how returning from the above function
cause write-out loop in commit to never terminate ?

If the current buffer is in the data_sync list of previous commiting
transaction, after returning from the journal_dirty_data,
generic_commit_write will redirty the buffer even though previous
commiting transaction commits the buffer to disk. Correct ?


-Ratna.
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