ext4-fix-namei-stack-usage

   1 ext4: Don't use 'struct dentry' for internal lookups
   2
   3 This is a port of a patch from Linus which fixes a 200+ byte stack
   4 usage problem in ext4_get_parent().
   5
   6 It's more efficient to pass down only the actual parts of the dentry
   7 that matter: the parent inode and the name, instead of allocating a
   8 struct dentry on the stack.
   9
  10 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  11 Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
  12 diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
  13 index a1f72d2..5295a92 100644
  14 --- a/fs/ext4/namei.c
  15 +++ b/fs/ext4/namei.c
  16 @@ -159,7 +159,7 @@ static void dx_set_count(struct dx_entry *entries, unsigned value);
  17  static void dx_set_limit(struct dx_entry *entries, unsigned value);
  18  static unsigned dx_root_limit(struct inode *dir, unsigned infosize);
  19  static unsigned dx_node_limit(struct inode *dir);
  20 -static struct dx_frame *dx_probe(struct dentry *dentry,
  21 +static struct dx_frame *dx_probe(const struct qstr *d_name,
  22                                  struct inode *dir,
  23                                  struct dx_hash_info *hinfo,
  24                                  struct dx_frame *frame,
  25 @@ -177,8 +177,10 @@ static int ext4_htree_next_block(struct inode *dir, __u32 hash,
  26                                  struct dx_frame *frame,
  27                                  struct dx_frame *frames,
  28                                  __u32 *start_hash);
  29 -static struct buffer_head * ext4_dx_find_entry(struct dentry *dentry,
  30 -                      struct ext4_dir_entry_2 **res_dir, int *err);
  31 +static struct buffer_head * ext4_dx_find_entry(struct inode *dir,
  32 +               const struct qstr *d_name,
  33 +               struct ext4_dir_entry_2 **res_dir,
  34 +               int *err);
  35  static int ext4_dx_add_entry(handle_t *handle, struct dentry *dentry,
  36                              struct inode *inode);
  37
  38 @@ -345,7 +347,7 @@ struct stats dx_show_entries(struct dx_hash_info *hinfo, struct inode *dir,
  39   * back to userspace.
  40   */
  41  static struct dx_frame *
  42 -dx_probe(struct dentry *dentry, struct inode *dir,
  43 +dx_probe(const struct qstr *d_name, struct inode *dir,
  44          struct dx_hash_info *hinfo, struct dx_frame *frame_in, int *err)
  45  {
  46         unsigned count, indirect;
  47 @@ -356,8 +358,6 @@ dx_probe(struct dentry *dentry, struct inode *dir,
  48         u32 hash;
  49
  50         frame->bh = NULL;
  51 -       if (dentry)
  52 -               dir = dentry->d_parent->d_inode;
  53         if (!(bh = ext4_bread (NULL,dir, 0, 0, err)))
  54                 goto fail;
  55         root = (struct dx_root *) bh->b_data;
  56 @@ -373,8 +373,8 @@ dx_probe(struct dentry *dentry, struct inode *dir,
  57         }
  58         hinfo->hash_version = root->info.hash_version;
  59         hinfo->seed = EXT4_SB(dir->i_sb)->s_hash_seed;
  60 -       if (dentry)
  61 -               ext4fs_dirhash(dentry->d_name.name, dentry->d_name.len, hinfo);
  62 +       if (d_name)
  63 +               ext4fs_dirhash(d_name->name, d_name->len, hinfo);
  64         hash = hinfo->hash;
  65
  66         if (root->info.unused_flags & 1) {
  67 @@ -649,7 +649,7 @@ int ext4_htree_fill_tree(struct file *dir_file, __u32 start_hash,
  68         }
  69         hinfo.hash = start_hash;
  70         hinfo.minor_hash = 0;
  71 -       frame = dx_probe(NULL, dir_file->f_path.dentry->d_inode, &hinfo, frames, &err);
  72 +       frame = dx_probe(NULL, dir, &hinfo, frames, &err);
  73         if (!frame)
  74                 return err;
  75
  76 @@ -805,15 +805,15 @@ static inline int ext4_match (int len, const char * const name,
  77   */
  78  static inline int search_dirblock(struct buffer_head *bh,
  79                                   struct inode *dir,
  80 -                                 struct dentry *dentry,
  81 +                                 const struct qstr *d_name,
  82                                   unsigned long offset,
  83                                   struct ext4_dir_entry_2 ** res_dir)
  84  {
  85         struct ext4_dir_entry_2 * de;
  86         char * dlimit;
  87         int de_len;
  88 -       const char *name = dentry->d_name.name;
  89 -       int namelen = dentry->d_name.len;
  90 +       const char *name = d_name->name;
  91 +       int namelen = d_name->len;
  92
  93         de = (struct ext4_dir_entry_2 *) bh->b_data;
  94         dlimit = bh->b_data + dir->i_sb->s_blocksize;
  95 @@ -852,7 +852,8 @@ static inline int search_dirblock(struct buffer_head *bh,
  96   * The returned buffer_head has ->b_count elevated.  The caller is expected
  97   * to brelse() it when appropriate.
  98   */
  99 -static struct buffer_head * ext4_find_entry (struct dentry *dentry,
 100 +static struct buffer_head * ext4_find_entry (struct inode *dir,
 101 +                                       const struct qstr *d_name,
 102                                         struct ext4_dir_entry_2 ** res_dir)
 103  {
 104         struct super_block *sb;
 105 @@ -866,16 +867,15 @@ static struct buffer_head * ext4_find_entry (struct dentry *dentry,
 106         int num = 0;
 107         ext4_lblk_t  nblocks;
 108         int i, err;
 109 -       struct inode *dir = dentry->d_parent->d_inode;
 110         int namelen;
 111
 112         *res_dir = NULL;
 113         sb = dir->i_sb;
 114 -       namelen = dentry->d_name.len;
 115 +       namelen = d_name->len;
 116         if (namelen > EXT4_NAME_LEN)
 117                 return NULL;
 118         if (is_dx(dir)) {
 119 -               bh = ext4_dx_find_entry(dentry, res_dir, &err);
 120 +               bh = ext4_dx_find_entry(dir, d_name, res_dir, &err);
 121                 /*
 122                  * On success, or if the error was file not found,
 123                  * return.  Otherwise, fall back to doing a search the
 124 @@ -928,7 +928,7 @@ restart:
 125                         brelse(bh);
 126                         goto next;
 127                 }
 128 -               i = search_dirblock(bh, dir, dentry,
 129 +               i = search_dirblock(bh, dir, d_name,
 130                             block << EXT4_BLOCK_SIZE_BITS(sb), res_dir);
 131                 if (i == 1) {
 132                         EXT4_I(dir)->i_dir_start_lookup = block;
 133 @@ -962,7 +962,7 @@ cleanup_and_exit:
 134         return ret;
 135  }
 136
 137 -static struct buffer_head * ext4_dx_find_entry(struct dentry *dentry,
 138 +static struct buffer_head * ext4_dx_find_entry(struct inode *dir, const struct qstr *d_name,
 139                        struct ext4_dir_entry_2 **res_dir, int *err)
 140  {
 141         struct super_block * sb;
 142 @@ -973,14 +973,13 @@ static struct buffer_head * ext4_dx_find_entry(struct dentry *dentry,
 143         struct buffer_head *bh;
 144         ext4_lblk_t block;
 145         int retval;
 146 -       int namelen = dentry->d_name.len;
 147 -       const u8 *name = dentry->d_name.name;
 148 -       struct inode *dir = dentry->d_parent->d_inode;
 149 +       int namelen = d_name->len;
 150 +       const u8 *name = d_name->name;
 151
 152         sb = dir->i_sb;
 153         /* NFS may look up ".." - look at dx_root directory block */
 154         if (namelen > 2 || name[0] != '.'||(name[1] != '.' && name[1] != '\0')){
 155 -               if (!(frame = dx_probe(dentry, NULL, &hinfo, frames, err)))
 156 +               if (!(frame = dx_probe(d_name, dir, &hinfo, frames, err)))
 157                         return NULL;
 158         } else {
 159                 frame = frames;
 160 @@ -1041,7 +1040,7 @@ static struct dentry *ext4_lookup(struct inode *dir, struct dentry *dentry, stru
 161         if (dentry->d_name.len > EXT4_NAME_LEN)
 162                 return ERR_PTR(-ENAMETOOLONG);
 163
 164 -       bh = ext4_find_entry(dentry, &de);
 165 +       bh = ext4_find_entry(dir, &dentry->d_name, &de);
 166         inode = NULL;
 167         if (bh) {
 168                 unsigned long ino = le32_to_cpu(de->inode);
 169 @@ -1064,15 +1063,14 @@ struct dentry *ext4_get_parent(struct dentry *child)
 170         unsigned long ino;
 171         struct dentry *parent;
 172         struct inode *inode;
 173 -       struct dentry dotdot;
 174 +       static const struct qstr dotdot = {
 175 +               .name = "..",
 176 +               .len = 2,
 177 +       };
 178         struct ext4_dir_entry_2 * de;
 179         struct buffer_head *bh;
 180
 181 -       dotdot.d_name.name = "..";
 182 -       dotdot.d_name.len = 2;
 183 -       dotdot.d_parent = child; /* confusing, isn't it! */
 184 -
 185 -       bh = ext4_find_entry(&dotdot, &de);
 186 +       bh = ext4_find_entry(child->d_inode, &dotdot, &de);
 187         inode = NULL;
 188         if (!bh)
 189                 return ERR_PTR(-ENOENT);
 190 @@ -1508,7 +1506,7 @@ static int ext4_dx_add_entry(handle_t *handle, struct dentry *dentry,
 191         struct ext4_dir_entry_2 *de;
 192         int err;
 193
 194 -       frame = dx_probe(dentry, NULL, &hinfo, frames, &err);
 195 +       frame = dx_probe(&dentry->d_name, dir, &hinfo, frames, &err);
 196         if (!frame)
 197                 return err;
 198         entries = frame->entries;
 199 @@ -2089,7 +2087,7 @@ static int ext4_rmdir(struct inode *dir, struct dentry *dentry)
 200                 return PTR_ERR(handle);
 201
 202         retval = -ENOENT;
 203 -       bh = ext4_find_entry(dentry, &de);
 204 +       bh = ext4_find_entry(dir, &dentry->d_name, &de);
 205         if (!bh)
 206                 goto end_rmdir;
 207
 208 @@ -2151,7 +2149,7 @@ static int ext4_unlink(struct inode *dir, struct dentry *dentry)
 209                 handle->h_sync = 1;
 210
 211         retval = -ENOENT;
 212 -       bh = ext4_find_entry(dentry, &de);
 213 +       bh = ext4_find_entry(dir, &dentry->d_name, &de);
 214         if (!bh)
 215                 goto end_unlink;
 216
 217 @@ -2312,7 +2310,7 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 218         if (IS_DIRSYNC(old_dir) || IS_DIRSYNC(new_dir))
 219                 handle->h_sync = 1;
 220
 221 -       old_bh = ext4_find_entry(old_dentry, &old_de);
 222 +       old_bh = ext4_find_entry(old_dir, &old_dentry->d_name, &old_de);
 223         /*
 224          *  Check for inode number is _not_ due to possible IO errors.
 225          *  We might rmdir the source, keep it as pwd of some process
 226 @@ -2325,7 +2323,7 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 227                 goto end_rename;
 228
 229         new_inode = new_dentry->d_inode;
 230 -       new_bh = ext4_find_entry(new_dentry, &new_de);
 231 +       new_bh = ext4_find_entry(new_dir, &new_dentry->d_name, &new_de);
 232         if (new_bh) {
 233                 if (!new_inode) {
 234                         brelse(new_bh);
 235 @@ -2392,7 +2390,7 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 236                 struct buffer_head *old_bh2;
 237                 struct ext4_dir_entry_2 *old_de2;
 238
 239 -               old_bh2 = ext4_find_entry(old_dentry, &old_de2);
 240 +               old_bh2 = ext4_find_entry(old_dir, &old_dentry->d_name, &old_de2);
 241                 if (old_bh2) {
 242                         retval = ext4_delete_entry(handle, old_dir,
 243                                                    old_de2, old_bh2);