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 This was reverted earlier due to a typo in the original commit where I
  10 experimented with using signal_pending() instead of
  11 fatal_signal_pending().  The test was in the wrong place if we were
  12 going to return signal_pending() since we would end up returning
  13 duplicant entries.  See 9f2394c9be47 for a more detailed explanation.
  14
  15 Added fix as suggested by Linus to check for signal_pending() in
  16 in the filldir() functions.
  17
  18 Reported-by: Benjamin LaHaise <bcrl@kvack.org>
  19 Google-Bug-Id: 27880676
  20 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  21 ---
  22  fs/compat.c     | 4 ++++
  23  fs/ext4/dir.c   | 5 +++++
  24  fs/ext4/namei.c | 5 +++++
  25  fs/readdir.c    | 4 ++++
  26  4 files changed, 18 insertions(+)
  27
  28 diff --git a/fs/compat.c b/fs/compat.c
  29 index a71936a..f940cb2 100644
  30 --- a/fs/compat.c
  31 +++ b/fs/compat.c
  32 @@ -936,6 +936,8 @@ static int compat_filldir(struct dir_context *ctx, const char *name, int namlen,
  33         }
  34         dirent = buf->previous;
  35         if (dirent) {
  36 +               if (signal_pending(current))
  37 +                       return -EINTR;
  38                 if (__put_user(offset, &dirent->d_off))
  39                         goto efault;
  40         }
  41 @@ -1020,6 +1022,8 @@ static int compat_filldir64(struct dir_context *ctx, const char *name,
  42         dirent = buf->previous;
  43
  44         if (dirent) {
  45 +               if (signal_pending(current))
  46 +                       return -EINTR;
  47                 if (__put_user_unaligned(offset, &dirent->d_off))
  48                         goto efault;
  49         }
  50 diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
  51 index 561d730..4173bfe 100644
  52 --- a/fs/ext4/dir.c
  53 +++ b/fs/ext4/dir.c
  54 @@ -150,6 +150,11 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
  55         while (ctx->pos < inode->i_size) {
  56                 struct ext4_map_blocks map;
  57
  58 +               if (fatal_signal_pending(current)) {
  59 +                       err = -ERESTARTSYS;
  60 +                       goto errout;
  61 +               }
  62 +               cond_resched();
  63                 map.m_lblk = ctx->pos >> EXT4_BLOCK_SIZE_BITS(sb);
  64                 map.m_len = 1;
  65                 err = ext4_map_blocks(NULL, inode, &map, 0);
  66 diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
  67 index 48e4b89..c07422d 100644
  68 --- a/fs/ext4/namei.c
  69 +++ b/fs/ext4/namei.c
  70 @@ -1107,6 +1107,11 @@ int ext4_htree_fill_tree(struct file *dir_file, __u32 start_hash,
  71         }
  72
  73         while (1) {
  74 +               if (fatal_signal_pending(current)) {
  75 +                       err = -ERESTARTSYS;
  76 +                       goto errout;
  77 +               }
  78 +               cond_resched();
  79                 block = dx_get_block(frame->at);
  80                 ret = htree_dirblock_to_tree(dir_file, dir, block, &hinfo,
  81                                              start_hash, start_minor_hash);
  82 diff --git a/fs/readdir.c b/fs/readdir.c
  83 index e69ef3b..5f2d4be 100644
  84 --- a/fs/readdir.c
  85 +++ b/fs/readdir.c
  86 @@ -169,6 +169,8 @@ static int filldir(struct dir_context *ctx, const char *name, int namlen,
  87         }
  88         dirent = buf->previous;
  89         if (dirent) {
  90 +               if (signal_pending(current))
  91 +                       return -EINTR;
  92                 if (__put_user(offset, &dirent->d_off))
  93                         goto efault;
  94         }
  95 @@ -248,6 +250,8 @@ static int filldir64(struct dir_context *ctx, const char *name, int namlen,
  96                 return -EINVAL;
  97         dirent = buf->previous;
  98         if (dirent) {
  99 +               if (signal_pending(current))
 100 +                       return -EINTR;
 101                 if (__put_user(offset, &dirent->d_off))
 102                         goto efault;
 103         }