fs: consolidate dentry kill sequence

The tricky locking for disposing of a dentry is duplicated 3 times in the
dcache (dput, pruning a dentry from the LRU, and pruning its ancestors).
Consolidate them all into a single function dentry_kill.

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

1 files changed, 61 insertions, 74 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index d1840b30c67..dc0551c9755 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -284,6 +284,40 @@ void d_drop(struct dentry *dentry)
 }
 EXPORT_SYMBOL(d_drop);
 
+/*
+ * Finish off a dentry we've decided to kill.
+ * dentry->d_lock must be held, returns with it unlocked.
+ * If ref is non-zero, then decrement the refcount too.
+ * Returns dentry requiring refcount drop, or NULL if we're done.
+ */
+static inline struct dentry *dentry_kill(struct dentry *dentry, int ref)
+        __releases(dentry->d_lock)
+{
+        struct dentry *parent;
+
+        if (!spin_trylock(&dcache_inode_lock)) {
+relock:
+                spin_unlock(&dentry->d_lock);
+                cpu_relax();
+                return dentry; /* try again with same dentry */
+        }
+        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;
+        }
+        if (ref)
+                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 then remove it */
+        __d_drop(dentry);
+        return d_kill(dentry, parent);
+}
+
 /* 
  * This is dput
  *
@@ -309,13 +343,9 @@ EXPORT_SYMBOL(d_drop);
  * call the dentry unlink method as well as removing it from the queues and
  * releasing its resources. If the parent dentries were scheduled for release
  * they too may now get deleted.
- *
- * no dcache lock, please.
  */
-
 void dput(struct dentry *dentry)
 {
-        struct dentry *parent;
         if (!dentry)
                 return;
 
@@ -348,26 +378,7 @@ repeat:
         return;
 
 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);
+        dentry = dentry_kill(dentry, 1);
         if (dentry)
                 goto repeat;
 }
@@ -563,51 +574,43 @@ restart:
 EXPORT_SYMBOL(d_prune_aliases);
 
 /*
- * Throw away a dentry - free the inode, dput the parent.  This requires that
- * the LRU list has already been removed.
+ * Try to throw away a dentry - free the inode, dput the parent.
+ * Requires dentry->d_lock is held, and dentry->d_count == 0.
+ * Releases dentry->d_lock.
  *
- * Try to prune ancestors as well.  This is necessary to prevent
- * quadratic behavior of shrink_dcache_parent(), but is also expected
- * to be beneficial in reducing dentry cache fragmentation.
+ * This may fail if locks cannot be acquired no problem, just try again.
  */
-static void prune_one_dentry(struct dentry *dentry, struct dentry *parent)
+static void try_prune_one_dentry(struct dentry *dentry)
         __releases(dentry->d_lock)
-        __releases(parent->d_lock)
-        __releases(dcache_inode_lock)
 {
-        __d_drop(dentry);
-        dentry = d_kill(dentry, parent);
+        struct dentry *parent;
 
+        parent = dentry_kill(dentry, 0);
         /*
-         * Prune ancestors.
+         * If dentry_kill returns NULL, we have nothing more to do.
+         * if it returns the same dentry, trylocks failed. In either
+         * case, just loop again.
+         *
+         * Otherwise, we need to prune ancestors too. This is necessary
+         * to prevent quadratic behavior of shrink_dcache_parent(), but
+         * is also expected to be beneficial in reducing dentry cache
+         * fragmentation.
          */
+        if (!parent)
+                return;
+        if (parent == dentry)
+                return;
+
+        /* Prune ancestors. */
+        dentry = parent;
         while (dentry) {
-relock:
                 spin_lock(&dentry->d_lock);
                 if (dentry->d_count > 1) {
                         dentry->d_count--;
                         spin_unlock(&dentry->d_lock);
                         return;
                 }
-                if (!spin_trylock(&dcache_inode_lock)) {
-relock2:
-                        spin_unlock(&dentry->d_lock);
-                        cpu_relax();
-                        goto relock;
-                }
-
-                if (IS_ROOT(dentry))
-                        parent = NULL;
-                else
-                        parent = dentry->d_parent;
-                if (parent && !spin_trylock(&parent->d_lock)) {
-                        spin_unlock(&dcache_inode_lock);
-                        goto relock2;
-                }
-                dentry->d_count--;
-                dentry_lru_del(dentry);
-                __d_drop(dentry);
-                dentry = d_kill(dentry, parent);
+                dentry = dentry_kill(dentry, 1);
         }
 }
 
@@ -617,8 +620,6 @@ static void shrink_dentry_list(struct list_head *list)
 
         rcu_read_lock();
         for (;;) {
-                struct dentry *parent;
-
                 dentry = list_entry_rcu(list->prev, struct dentry, d_lru);
                 if (&dentry->d_lru == list)
                         break; /* empty */
@@ -639,24 +640,10 @@ static void shrink_dentry_list(struct list_head *list)
                         continue;
                 }
 
-                if (!spin_trylock(&dcache_inode_lock)) {
-relock:
-                        spin_unlock(&dentry->d_lock);
-                        cpu_relax();
-                        continue;
-                }
-                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_lru_del(dentry);
-
                 rcu_read_unlock();
-                prune_one_dentry(dentry, parent);
+
+                try_prune_one_dentry(dentry);
+
                 rcu_read_lock();
         }
         rcu_read_unlock();