linux-ext4 - [PATCH 19/20] vfs: Handle case-exact lookup in d_add

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Message-Id: <20180703170700.9306-20-krisman@collabora.co.uk>
Date:   Tue,  3 Jul 2018 13:06:59 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.co.uk>
To:     tytso@....edu
Cc:     linux-ext4@...r.kernel.org, darrick.wong@...cle.com,
        kernel@...labora.com,
        Gabriel Krisman Bertazi <krisman@...labora.co.uk>
Subject: [PATCH 19/20] vfs: Handle case-exact lookup in d_add_ci

This prevents a soft hang if called d_add_ci is called from the FS
layer, when doing a CI search but the result dentry is the exact match.

Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.co.uk>
---
 fs/dcache.c | 33 ++++++++++++++++++---------------
 1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 0e8e5de3c48a..3b55023cca7e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2059,6 +2059,20 @@ struct dentry *d_obtain_root(struct inode *inode)
 }
 EXPORT_SYMBOL(d_obtain_root);
 
+static inline bool d_same_name(const struct dentry *dentry,
+				const struct dentry *parent,
+				const struct qstr *name)
+{
+	if (likely(!(parent->d_flags & DCACHE_OP_COMPARE))) {
+		if (dentry->d_name.len != name->len)
+			return false;
+		return dentry_cmp(dentry, name->name, name->len) == 0;
+	}
+	return parent->d_op->d_compare(dentry,
+				       dentry->d_name.len, dentry->d_name.name,
+				       name) == 0;
+}
+
 /**
  * d_add_ci - lookup or allocate new dentry with case-exact name
  * @inode:  the inode case-insensitive lookup has found
@@ -2080,6 +2094,10 @@ struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
 {
 	struct dentry *found, *res;
 
+	/* Trivial case: CI search is exact match.  */
+	if (d_same_name(dentry, dentry->d_parent, name))
+		return d_splice_alias(inode, dentry);
+
 	/*
 	 * First check if a dentry matching the name already exists,
 	 * if not go ahead and create it now.
@@ -2112,21 +2130,6 @@ struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
 }
 EXPORT_SYMBOL(d_add_ci);
 
-
-static inline bool d_same_name(const struct dentry *dentry,
-				const struct dentry *parent,
-				const struct qstr *name)
-{
-	if (likely(!(parent->d_flags & DCACHE_OP_COMPARE))) {
-		if (dentry->d_name.len != name->len)
-			return false;
-		return dentry_cmp(dentry, name->name, name->len) == 0;
-	}
-	return parent->d_op->d_compare(dentry,
-				       dentry->d_name.len, dentry->d_name.name,
-				       name) == 0;
-}
-
 /**
  * __d_lookup_rcu - search for a dentry (racy, store-free)
  * @parent: parent dentry
-- 
2.18.0