LU-645 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: Ib891e7d2e5ae7efe19ef2ac0abb111e9f9681b7b
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1435
Tested-by: Hudson
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>

diff --git a/lustre/llite/dcache.c b/lustre/llite/dcache.c
index 916b0ed..782047e 100644 (file)
--- a/lustre/llite/dcache.c
+++ b/lustre/llite/dcache.c
@@ -533,10 +533,8 @@ revalidate_finish:
          * dentry */
         spin_lock(&ll_lookup_lock);
         spin_lock(&dcache_lock);
-        lock_dentry(de);
-        __d_drop(de);
-        unlock_dentry(de);
-        d_rehash_cond(de, 0);
+        if (d_unhashed(de))
+                d_rehash_cond(de, 0);
         spin_unlock(&dcache_lock);
         spin_unlock(&ll_lookup_lock);
 

diff --git a/lustre/llite/namei.c b/lustre/llite/namei.c
index 87849b3..7f0c7e3 100644 (file)
--- a/lustre/llite/namei.c
+++ b/lustre/llite/namei.c
@@ -450,11 +450,9 @@ static struct dentry *ll_find_alias(struct inode *inode, struct dentry *de)
                         continue;
 
                 dget_locked(dentry);
-                lock_dentry(dentry);
-                __d_drop(dentry);
-                unlock_dentry(dentry);
                 ll_dops_init(dentry, 0, 1);
-                d_rehash_cond(dentry, 0); /* avoid taking dcache_lock inside */
+                if (d_unhashed(dentry))
+                        d_rehash_cond(dentry, 0); /* avoid taking dcache_lock inside */
                 spin_unlock(&dcache_lock);
                 spin_unlock(&ll_lookup_lock);
                 iput(inode);

diff --git a/lustre/llite/statahead.c b/lustre/llite/statahead.c
index b415dc9..d874286 100644 (file)
--- a/lustre/llite/statahead.c
+++ b/lustre/llite/statahead.c
@@ -452,10 +452,10 @@ static int do_statahead_interpret(struct ll_statahead_info *sai)
                 spin_lock(&ll_lookup_lock);
                 spin_lock(&dcache_lock);
                 lock_dentry(dentry);
-                __d_drop(dentry);
                 dentry->d_flags &= ~DCACHE_LUSTRE_INVALID;
                 unlock_dentry(dentry);
-                d_rehash_cond(dentry, 0);
+                if (d_unhashed(dentry))
+                        d_rehash_cond(dentry, 0);
                 spin_unlock(&dcache_lock);
                 spin_unlock(&ll_lookup_lock);