ext4: Don't use 'struct dentry' for internal lookups

This is a port of a patch from Linus which fixes a 200+ byte stack
usage problem in ext4_get_parent().

It's more efficient to pass down only the actual parts of the dentry
that matter: the parent inode and the name, instead of allocating a
struct dentry on the stack.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 33 insertions, 35 deletions

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index a1f72d217c7c..5295a9225cf9 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -159,7 +159,7 @@ static void dx_set_count(struct dx_entry *entries, unsigned value);
 static void dx_set_limit(struct dx_entry *entries, unsigned value);
 static unsigned dx_root_limit(struct inode *dir, unsigned infosize);
 static unsigned dx_node_limit(struct inode *dir);
-static struct dx_frame *dx_probe(struct dentry *dentry,
+static struct dx_frame *dx_probe(const struct qstr *d_name,
                                  struct inode *dir,
                                  struct dx_hash_info *hinfo,
                                  struct dx_frame *frame,
@@ -177,8 +177,10 @@ static int ext4_htree_next_block(struct inode *dir, __u32 hash,
                                  struct dx_frame *frame,
                                  struct dx_frame *frames,
                                  __u32 *start_hash);
-static struct buffer_head * ext4_dx_find_entry(struct dentry *dentry,
-                       struct ext4_dir_entry_2 **res_dir, int *err);
+static struct buffer_head * ext4_dx_find_entry(struct inode *dir,
+                const struct qstr *d_name,
+                struct ext4_dir_entry_2 **res_dir,
+                int *err);
 static int ext4_dx_add_entry(handle_t *handle, struct dentry *dentry,
                              struct inode *inode);
 
@@ -345,7 +347,7 @@ struct stats dx_show_entries(struct dx_hash_info *hinfo, struct inode *dir,
  * back to userspace.
  */
 static struct dx_frame *
-dx_probe(struct dentry *dentry, struct inode *dir,
+dx_probe(const struct qstr *d_name, struct inode *dir,
          struct dx_hash_info *hinfo, struct dx_frame *frame_in, int *err)
 {
         unsigned count, indirect;
@@ -356,8 +358,6 @@ dx_probe(struct dentry *dentry, struct inode *dir,
         u32 hash;
 
         frame->bh = NULL;
-        if (dentry)
-                dir = dentry->d_parent->d_inode;
         if (!(bh = ext4_bread (NULL,dir, 0, 0, err)))
                 goto fail;
         root = (struct dx_root *) bh->b_data;
@@ -373,8 +373,8 @@ dx_probe(struct dentry *dentry, struct inode *dir,
         }
         hinfo->hash_version = root->info.hash_version;
         hinfo->seed = EXT4_SB(dir->i_sb)->s_hash_seed;
-        if (dentry)
-                ext4fs_dirhash(dentry->d_name.name, dentry->d_name.len, hinfo);
+        if (d_name)
+                ext4fs_dirhash(d_name->name, d_name->len, hinfo);
         hash = hinfo->hash;
 
         if (root->info.unused_flags & 1) {
@@ -649,7 +649,7 @@ int ext4_htree_fill_tree(struct file *dir_file, __u32 start_hash,
         }
         hinfo.hash = start_hash;
         hinfo.minor_hash = 0;
-        frame = dx_probe(NULL, dir_file->f_path.dentry->d_inode, &hinfo, frames, &err);
+        frame = dx_probe(NULL, dir, &hinfo, frames, &err);
         if (!frame)
                 return err;
 
@@ -805,15 +805,15 @@ static inline int ext4_match (int len, const char * const name,
  */
 static inline int search_dirblock(struct buffer_head *bh,
                                   struct inode *dir,
-                                  struct dentry *dentry,
+                                  const struct qstr *d_name,
                                   unsigned long offset,
                                   struct ext4_dir_entry_2 ** res_dir)
 {
         struct ext4_dir_entry_2 * de;
         char * dlimit;
         int de_len;
-        const char *name = dentry->d_name.name;
-        int namelen = dentry->d_name.len;
+        const char *name = d_name->name;
+        int namelen = d_name->len;
 
         de = (struct ext4_dir_entry_2 *) bh->b_data;
         dlimit = bh->b_data + dir->i_sb->s_blocksize;
@@ -852,7 +852,8 @@ static inline int search_dirblock(struct buffer_head *bh,
  * The returned buffer_head has ->b_count elevated.  The caller is expected
  * to brelse() it when appropriate.
  */
-static struct buffer_head * ext4_find_entry (struct dentry *dentry,
+static struct buffer_head * ext4_find_entry (struct inode *dir,
+                                        const struct qstr *d_name,
                                         struct ext4_dir_entry_2 ** res_dir)
 {
         struct super_block *sb;
@@ -866,16 +867,15 @@ static struct buffer_head * ext4_find_entry (struct dentry *dentry,
         int num = 0;
         ext4_lblk_t  nblocks;
         int i, err;
-        struct inode *dir = dentry->d_parent->d_inode;
         int namelen;
 
         *res_dir = NULL;
         sb = dir->i_sb;
-        namelen = dentry->d_name.len;
+        namelen = d_name->len;
         if (namelen > EXT4_NAME_LEN)
                 return NULL;
         if (is_dx(dir)) {
-                bh = ext4_dx_find_entry(dentry, res_dir, &err);
+                bh = ext4_dx_find_entry(dir, d_name, res_dir, &err);
                 /*
                  * On success, or if the error was file not found,
                  * return.  Otherwise, fall back to doing a search the
@@ -928,7 +928,7 @@ restart:
                         brelse(bh);
                         goto next;
                 }
-                i = search_dirblock(bh, dir, dentry,
+                i = search_dirblock(bh, dir, d_name,
                             block << EXT4_BLOCK_SIZE_BITS(sb), res_dir);
                 if (i == 1) {
                         EXT4_I(dir)->i_dir_start_lookup = block;
@@ -962,7 +962,7 @@ cleanup_and_exit:
         return ret;
 }
 
-static struct buffer_head * ext4_dx_find_entry(struct dentry *dentry,
+static struct buffer_head * ext4_dx_find_entry(struct inode *dir, const struct qstr *d_name,
                        struct ext4_dir_entry_2 **res_dir, int *err)
 {
         struct super_block * sb;
@@ -973,14 +973,13 @@ static struct buffer_head * ext4_dx_find_entry(struct dentry *dentry,
         struct buffer_head *bh;
         ext4_lblk_t block;
         int retval;
-        int namelen = dentry->d_name.len;
-        const u8 *name = dentry->d_name.name;
-        struct inode *dir = dentry->d_parent->d_inode;
+        int namelen = d_name->len;
+        const u8 *name = d_name->name;
 
         sb = dir->i_sb;
         /* NFS may look up ".." - look at dx_root directory block */
         if (namelen > 2 || name[0] != '.'||(name[1] != '.' && name[1] != '\0')){
-                if (!(frame = dx_probe(dentry, NULL, &hinfo, frames, err)))
+                if (!(frame = dx_probe(d_name, dir, &hinfo, frames, err)))
                         return NULL;
         } else {
                 frame = frames;
@@ -1041,7 +1040,7 @@ static struct dentry *ext4_lookup(struct inode *dir, struct dentry *dentry, stru
         if (dentry->d_name.len > EXT4_NAME_LEN)
                 return ERR_PTR(-ENAMETOOLONG);
 
-        bh = ext4_find_entry(dentry, &de);
+        bh = ext4_find_entry(dir, &dentry->d_name, &de);
         inode = NULL;
         if (bh) {
                 unsigned long ino = le32_to_cpu(de->inode);
@@ -1064,15 +1063,14 @@ struct dentry *ext4_get_parent(struct dentry *child)
         unsigned long ino;
         struct dentry *parent;
         struct inode *inode;
-        struct dentry dotdot;
+        static const struct qstr dotdot = {
+                .name = "..",
+                .len = 2,
+        };
         struct ext4_dir_entry_2 * de;
         struct buffer_head *bh;
 
-        dotdot.d_name.name = "..";
-        dotdot.d_name.len = 2;
-        dotdot.d_parent = child; /* confusing, isn't it! */
-
-        bh = ext4_find_entry(&dotdot, &de);
+        bh = ext4_find_entry(child->d_inode, &dotdot, &de);
         inode = NULL;
         if (!bh)
                 return ERR_PTR(-ENOENT);
@@ -1508,7 +1506,7 @@ static int ext4_dx_add_entry(handle_t *handle, struct dentry *dentry,
         struct ext4_dir_entry_2 *de;
         int err;
 
-        frame = dx_probe(dentry, NULL, &hinfo, frames, &err);
+        frame = dx_probe(&dentry->d_name, dir, &hinfo, frames, &err);
         if (!frame)
                 return err;
         entries = frame->entries;
@@ -2089,7 +2087,7 @@ static int ext4_rmdir(struct inode *dir, struct dentry *dentry)
                 return PTR_ERR(handle);
 
         retval = -ENOENT;
-        bh = ext4_find_entry(dentry, &de);
+        bh = ext4_find_entry(dir, &dentry->d_name, &de);
         if (!bh)
                 goto end_rmdir;
 
@@ -2151,7 +2149,7 @@ static int ext4_unlink(struct inode *dir, struct dentry *dentry)
                 handle->h_sync = 1;
 
         retval = -ENOENT;
-        bh = ext4_find_entry(dentry, &de);
+        bh = ext4_find_entry(dir, &dentry->d_name, &de);
         if (!bh)
                 goto end_unlink;
 
@@ -2312,7 +2310,7 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
         if (IS_DIRSYNC(old_dir) || IS_DIRSYNC(new_dir))
                 handle->h_sync = 1;
 
-        old_bh = ext4_find_entry(old_dentry, &old_de);
+        old_bh = ext4_find_entry(old_dir, &old_dentry->d_name, &old_de);
         /*
          *  Check for inode number is _not_ due to possible IO errors.
          *  We might rmdir the source, keep it as pwd of some process
@@ -2325,7 +2323,7 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
                 goto end_rename;
 
         new_inode = new_dentry->d_inode;
-        new_bh = ext4_find_entry(new_dentry, &new_de);
+        new_bh = ext4_find_entry(new_dir, &new_dentry->d_name, &new_de);
         if (new_bh) {
                 if (!new_inode) {
                         brelse(new_bh);
@@ -2392,7 +2390,7 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
                 struct buffer_head *old_bh2;
                 struct ext4_dir_entry_2 *old_de2;
 
-                old_bh2 = ext4_find_entry(old_dentry, &old_de2);
+                old_bh2 = ext4_find_entry(old_dir, &old_dentry->d_name, &old_de2);
                 if (old_bh2) {
                         retval = ext4_delete_entry(handle, old_dir,
                                                    old_de2, old_bh2);