kill-the-BKL/reiserfs: release write lock on fs_changed()

fs_changed() is a macro used by reiserfs to check whether its tree has been
rebalanced. It has been designed to check parallel changes on the tree after
calling a sleeping function, which released the Bkl.

fs_changed() also calls cond_resched(), so that if rescheduling is needed,
we are in the best place to do that, since we check if the tree has changed
just after (because of the bkl release on schedule()).

Even if we are not anymore using the Bkl, we still want to release the lock
while we reschedule, so that other waiters for the lock can acquire it safely,
because of the following __fs_changed() check.

[ Impact: release the reiserfs write lock when it is not needed ]

Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

diff --git a/include/linux/reiserfs_fs.h b/include/linux/reiserfs_fs.h
index 4a2df57c8b1d590ba2f9226e358d2e413a3917ca..fa5dbf307c40de0fd48e5fe5fdba863308c62427 100644 (file)
--- a/include/linux/reiserfs_fs.h
+++ b/include/linux/reiserfs_fs.h
@@ -1333,7 +1333,13 @@ static inline loff_t max_reiserfs_offset(struct inode *inode)
 #define get_generation(s) atomic_read (&fs_generation(s))
 #define FILESYSTEM_CHANGED_TB(tb)  (get_generation((tb)->tb_sb) != (tb)->fs_gen)
 #define __fs_changed(gen,s) (gen != get_generation (s))
-#define fs_changed(gen,s) ({cond_resched(); __fs_changed(gen, s);})
+#define fs_changed(gen,s)              \
+({                                     \
+       reiserfs_write_unlock(s);       \
+       cond_resched();                 \
+       reiserfs_write_lock(s);         \
+       __fs_changed(gen, s);           \
+})
 
 /***************************************************************************/
 /*                  FIXATE NODES                                           */