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Subject[PATCH 7/7] kill-the-bkl/reiserfs: use mutex_lock in reiserfs_mutex_lock_safe
Date
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@suse.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.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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