allow-resched-and-interruption-of-large-empty-directories

   1 ext4: allow readdir()'s of large empty directories to be interrupted
   2
   3 If a directory has a large number of empty blocks, iterating over all
   4 of them can take a long time, leading to scheduler warnings and users
   5 getting irritated when they can't kill a process in the middle of one
   6 of these long-running readdir operations.  Fix this by adding checks to
   7 ext4_readdir() and ext4_htree_fill_tree().
   8
   9 Reported-by: Benjamin LaHaise <bcrl@kvack.org>
  10 Google-Bug-Id: 27880676
  11 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  12 ---
  13  fs/ext4/dir.c   | 5 +++++
  14  fs/ext4/namei.c | 5 +++++
  15  2 files changed, 10 insertions(+)
  16
  17 diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
  18 index 33f5e2a..ebfcb89 100644
  19 --- a/fs/ext4/dir.c
  20 +++ b/fs/ext4/dir.c
  21 @@ -150,6 +150,11 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
  22         while (ctx->pos < inode->i_size) {
  23                 struct ext4_map_blocks map;
  24
  25 +               if (fatal_signal_pending(current)) {
  26 +                       err = -ERESTARTSYS;
  27 +                       goto errout;
  28 +               }
  29 +               cond_resched();
  30                 map.m_lblk = ctx->pos >> EXT4_BLOCK_SIZE_BITS(sb);
  31                 map.m_len = 1;
  32                 err = ext4_map_blocks(NULL, inode, &map, 0);
  33 diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
  34 index 48e4b89..db98f89f 100644
  35 --- a/fs/ext4/namei.c
  36 +++ b/fs/ext4/namei.c
  37 @@ -1107,6 +1107,11 @@ int ext4_htree_fill_tree(struct file *dir_file, __u32 start_hash,
  38         }
  39
  40         while (1) {
  41 +               if (signal_pending(current)) {
  42 +                       err = -ERESTARTSYS;
  43 +                       goto errout;
  44 +               }
  45 +               cond_resched();
  46                 block = dx_get_block(frame->at);
  47                 ret = htree_dirblock_to_tree(dir_file, dir, block, &hinfo,
  48                                              start_hash, start_minor_hash);