LU-645 llite: Avoid unnecessary dentry rehashing

In patchless case the sequence __d_drop() then d_rehash_cond() creates
race window if dentry is already hashed, in this case rehashing should
be avoided.

Change-Id: I59e035c6d19b869955e66fb010c1b137d0aab0ec
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1434
Tested-by: Hudson
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>

diff --git a/lustre/llite/llite_internal.h b/lustre/llite/llite_internal.h
index a7b314b..7b89ca9 100644 (file)
--- a/lustre/llite/llite_internal.h
+++ b/lustre/llite/llite_internal.h
@@ -1361,10 +1361,8 @@ static inline void ll_dentry_rehash(struct dentry *dentry, int locked)
                 cfs_spin_lock(&ll_lookup_lock);
                 spin_lock(&dcache_lock);
         }
-        lock_dentry(dentry);
-        __d_drop(dentry);
-        unlock_dentry(dentry);
-        d_rehash_cond(dentry, 0);
+        if (d_unhashed(dentry))
+                d_rehash_cond(dentry, 0);
         if (!locked) {
                 spin_unlock(&dcache_lock);
                 cfs_spin_unlock(&ll_lookup_lock);