linux-ext4 - [PATCH 1/2] jbd2: don't call get_bh() before calling __jbd2_journal_remove

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Date:	Tue,  2 Sep 2014 18:46:39 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	Theodore Ts'o <tytso@....edu>
Subject: [PATCH 1/2] jbd2: don't call get_bh() before calling __jbd2_journal_remove_checkpoint()

The __jbd2_journal_remove_checkpoint() doesn't require an elevated
b_count; indeed, until the jh structure gets released by the call to
jbd2_journal_put_journal_head(), the bh's b_count is elevated by
virtue of the existence of the jh structure.

Suggested-by: Jan Kara <jack@...e.cz>
Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 fs/jbd2/checkpoint.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 22fcd50..cb6e17c 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -100,11 +100,8 @@ static int __try_to_free_cp_buf(struct journal_head *jh)
 		 * Get our reference so that bh cannot be freed before
 		 * we unlock it
 		 */
-		get_bh(bh);
 		JBUFFER_TRACE(jh, "remove from checkpoint list");
 		ret = __jbd2_journal_remove_checkpoint(jh) + 1;
-		BUFFER_TRACE(bh, "release");
-		__brelse(bh);
 	}
 	return ret;
 }
@@ -216,7 +213,7 @@ int jbd2_log_do_checkpoint(journal_t *journal)
 	struct buffer_head	*bh;
 	transaction_t		*transaction;
 	tid_t			this_tid;
-	int			result, batch_count = 0, done = 0;
+	int			result, batch_count = 0;
 
 	jbd_debug(1, "Start checkpoint\n");
 
@@ -291,11 +288,9 @@ restart:
 		if (!buffer_dirty(bh)) {
 			if (unlikely(buffer_write_io_error(bh)) && !result)
 				result = -EIO;
-			get_bh(bh);
 			BUFFER_TRACE(bh, "remove from checkpoint");
 			__jbd2_journal_remove_checkpoint(jh);
 			spin_unlock(&journal->j_list_lock);
-			__brelse(bh);
 			goto retry;
 		}
 		/*
@@ -338,7 +333,7 @@ restart2:
 	    transaction->t_tid != this_tid)
 		goto out;
 
-	while (!done && transaction->t_checkpoint_io_list) {
+	while (transaction->t_checkpoint_io_list) {
 		jh = transaction->t_checkpoint_io_list;
 		bh = jh2bh(jh);
 		get_bh(bh);
@@ -359,8 +354,9 @@ restart2:
 		 * know that it has been written out and so we can
 		 * drop it from the list
 		 */
-		done = __jbd2_journal_remove_checkpoint(jh);
 		__brelse(bh);
+		if (__jbd2_journal_remove_checkpoint(jh))
+			break;
 	}
 out:
 	spin_unlock(&journal->j_list_lock);
-- 
2.1.0

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