Many years ago it was the case that a

	while (1) {
		write(fd, buf, 1);
		lseek(fd, 0, SEEK_SET);
	}

would livelock kjournald because kjournald could never clean all the buffers
on the transaction's list.

So I put some code in journal_dirty_data() to detect this and to block the
write() caller.  It can cause unpleasant latencies under some circumstances.

With the dual list writeout arrangement in journal_commit_transaction() the
livelock is no longer possible so we can remove this code.


---

 25-akpm/fs/jbd/transaction.c |   23 -----------------------
 1 files changed, 23 deletions(-)

diff -puN fs/jbd/transaction.c~jbd-remove-livelock-avoidance fs/jbd/transaction.c
--- 25/fs/jbd/transaction.c~jbd-remove-livelock-avoidance	2004-03-18 18:20:04.331865880 -0800
+++ 25-akpm/fs/jbd/transaction.c	2004-03-18 18:20:46.906393568 -0800
@@ -931,7 +931,6 @@ out:
 int journal_dirty_data(handle_t *handle, struct buffer_head *bh)
 {
 	journal_t *journal = handle->h_transaction->t_journal;
-	int need_brelse = 0;
 	struct journal_head *jh;
 
 	if (is_handle_aborted(handle))
@@ -1016,24 +1015,6 @@ int journal_dirty_data(handle_t *handle,
 				goto no_journal;
 			}
 
-			/*
-			 * 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 */
-			}
-
 			/* journal_clean_data_list() may have got there first */
 			if (jh->b_transaction != NULL) {
 				JBUFFER_TRACE(jh, "unfile from commit");
@@ -1065,10 +1046,6 @@ int journal_dirty_data(handle_t *handle,
 no_journal:
 	spin_unlock(&journal->j_list_lock);
 	jbd_unlock_bh_state(bh);
-	if (need_brelse) {
-		BUFFER_TRACE(bh, "brelse");
-		__brelse(bh);
-	}
 	JBUFFER_TRACE(jh, "exit");
 	journal_put_journal_head(jh);
 	return 0;

_