fs: dcache reduce dput locking

It is possible to run dput without taking data structure locks up-front. In
many cases where we don't kill the dentry anyway, these locks are not required.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

1 files changed, 23 insertions, 29 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index bf6294a20f0e..98a05696593e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -323,35 +323,16 @@ repeat:
         if (dentry->d_count == 1)
                 might_sleep();
         spin_lock(&dentry->d_lock);
-        if (IS_ROOT(dentry))
-                parent = NULL;
-        else
-                parent = dentry->d_parent;
-        if (dentry->d_count == 1) {
-                if (!spin_trylock(&dcache_inode_lock)) {
-drop2:
-                        spin_unlock(&dentry->d_lock);
-                        goto repeat;
-                }
-                if (parent && !spin_trylock(&parent->d_lock)) {
-                        spin_unlock(&dcache_inode_lock);
-                        goto drop2;
-                }
-        }
-        dentry->d_count--;
-        if (dentry->d_count) {
+        BUG_ON(!dentry->d_count);
+        if (dentry->d_count > 1) {
+                dentry->d_count--;
                 spin_unlock(&dentry->d_lock);
-                if (parent)
-                        spin_unlock(&parent->d_lock);
                 return;
         }
 
-        /*
-         * AV: ->d_delete() is _NOT_ allowed to block now.
-         */
         if (dentry->d_op && dentry->d_op->d_delete) {
                 if (dentry->d_op->d_delete(dentry))
-                        goto unhash_it;
+                        goto kill_it;
         }
 
         /* Unreachable? Get rid of it */
@@ -362,17 +343,30 @@ drop2:
         dentry->d_flags |= DCACHE_REFERENCED;
         dentry_lru_add(dentry);
 
-        spin_unlock(&dentry->d_lock);
-        if (parent)
-                spin_unlock(&parent->d_lock);
-        spin_unlock(&dcache_inode_lock);
+        dentry->d_count--;
+        spin_unlock(&dentry->d_lock);
         return;
 
-unhash_it:
-        __d_drop(dentry);
 kill_it:
+        if (!spin_trylock(&dcache_inode_lock)) {
+relock:
+                spin_unlock(&dentry->d_lock);
+                cpu_relax();
+                goto repeat;
+        }
+        if (IS_ROOT(dentry))
+                parent = NULL;
+        else
+                parent = dentry->d_parent;
+        if (parent && !spin_trylock(&parent->d_lock)) {
+                spin_unlock(&dcache_inode_lock);
+                goto relock;
+        }
+        dentry->d_count--;
         /* if dentry was on the d_lru list delete it from there */
         dentry_lru_del(dentry);
+        /* if it was on the hash (d_delete case), then remove it */
+        __d_drop(dentry);
         dentry = d_kill(dentry, parent);
         if (dentry)
                 goto repeat;