linux-kernel - [PATCH 3.14 40/44] dcache: dont need rcu in shrink_dentry

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Date:	Fri, 14 Aug 2015 10:45:17 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Miklos Szeredi <mszeredi@...e.cz>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Subject: [PATCH 3.14 40/44] dcache: dont need rcu in shrink_dentry_list()

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@...e.cz>

commit 60942f2f235ce7b817166cdf355eed729094834d upstream.

Since now the shrink list is private and nobody can free the dentry while
it is on the shrink list, we can remove RCU protection from this.

Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Cc: "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/dcache.c |   27 ++++-----------------------
 1 file changed, 4 insertions(+), 23 deletions(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -797,23 +797,9 @@ static void shrink_dentry_list(struct li
 {
 	struct dentry *dentry, *parent;
 
-	rcu_read_lock();
-	for (;;) {
-		dentry = list_entry_rcu(list->prev, struct dentry, d_lru);
-		if (&dentry->d_lru == list)
-			break; /* empty */
-
-		/*
-		 * Get the dentry lock, and re-verify that the dentry is
-		 * this on the shrinking list. If it is, we know that
-		 * DCACHE_SHRINK_LIST and DCACHE_LRU_LIST are set.
-		 */
+	while (!list_empty(list)) {
+		dentry = list_entry(list->prev, struct dentry, d_lru);
 		spin_lock(&dentry->d_lock);
-		if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
-			spin_unlock(&dentry->d_lock);
-			continue;
-		}
-
 		/*
 		 * The dispose list is isolated and dentries are not accounted
 		 * to the LRU here, so we can simply remove it from the list
@@ -829,23 +815,20 @@ static void shrink_dentry_list(struct li
 			spin_unlock(&dentry->d_lock);
 			continue;
 		}
-		rcu_read_unlock();
 
 		parent = dentry_kill(dentry, 0);
 		/*
 		 * If dentry_kill returns NULL, we have nothing more to do.
 		 */
-		if (!parent) {
-			rcu_read_lock();
+		if (!parent)
 			continue;
-		}
+
 		if (unlikely(parent == dentry)) {
 			/*
 			 * trylocks have failed and d_lock has been held the
 			 * whole time, so it could not have been added to any
 			 * other lists. Just add it back to the shrink list.
 			 */
-			rcu_read_lock();
 			d_shrink_add(dentry, list);
 			spin_unlock(&dentry->d_lock);
 			continue;
@@ -859,9 +842,7 @@ static void shrink_dentry_list(struct li
 		dentry = parent;
 		while (dentry && !lockref_put_or_lock(&dentry->d_lockref))
 			dentry = dentry_kill(dentry, 1);
-		rcu_read_lock();
 	}
-	rcu_read_unlock();
 }
 
 static enum lru_status


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