linux-kernel - [PATCH 7/7] kill-the-bkl/reiserfs: use mutex_lock in reiserfs_mutex_lock

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Date:	Fri,  8 May 2009 20:35:24 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jeff Mahoney <jeffm@...e.com>,
	Chris Mason <chris.mason@...cle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Alexander Beregalov <a.beregalov@...il.com>
Subject: [PATCH 7/7] kill-the-bkl/reiserfs: use mutex_lock in reiserfs_mutex_lock_safe

reiserfs_mutex_lock_safe() is a hack to avoid any dependency between
an internal reiserfs mutex and the write lock, it has been proposed
to follow the old bkl logic.

The code does the following:

while (!mutex_trylock(m)) {
	reiserfs_write_unlock(s);
	schedule();
	reiserfs_write_lock(s);
}

It then imitate the implicit behaviour of the lock when it was
a Bkl and hadn't such dependency:

mutex_lock(m) {
	if (fastpath)
		let's go
	else {
		wait_for_mutex() {
			schedule() {
				unlock_kernel()
				reacquire_lock_kernel()
			}
		}
	}
}

The problem is that by using such explicit schedule(), we don't
benefit of the adaptive mutex spinning on owner.

The logic in use now is:

reiserfs_write_unlock(s);
mutex_lock(m); // -> possible adaptive spinning
reiserfs_write_lock(s);

[ Impact: restore the use of adaptive spinning mutexes in reiserfs ]

Cc: Jeff Mahoney <jeffm@...e.com>
Cc: Chris Mason <chris.mason@...cle.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Alexander Beregalov <a.beregalov@...il.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
 fs/reiserfs/journal.c |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
index b1ebd5a..3c3e00d 100644
--- a/fs/reiserfs/journal.c
+++ b/fs/reiserfs/journal.c
@@ -566,11 +566,9 @@ static inline void insert_journal_hash(struct reiserfs_journal_cnode **table,
 static inline void reiserfs_mutex_lock_safe(struct mutex *m,
 			       struct super_block *s)
 {
-	while (!mutex_trylock(m)) {
-		reiserfs_write_unlock(s);
-		schedule();
-		reiserfs_write_lock(s);
-	}
+	reiserfs_write_unlock(s);
+	mutex_lock(m);
+	reiserfs_write_lock(s);
 }
 
 /* lock the current transaction */
-- 
1.6.2.3

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