queue-4.19/tmpfs-fix-link-accounting-when-a-tmpfile-is-linked-i.patch

   1 From 8fb0b5fc39a4bed3c13af179633fb4a517de42d7 Mon Sep 17 00:00:00 2001
   2 From: "Darrick J. Wong" <darrick.wong@oracle.com>
   3 Date: Thu, 21 Feb 2019 08:48:09 -0800
   4 Subject: tmpfs: fix link accounting when a tmpfile is linked in
   5
   6 [ Upstream commit 1062af920c07f5b54cf5060fde3339da6df0cf6b ]
   7
   8 tmpfs has a peculiarity of accounting hard links as if they were
   9 separate inodes: so that when the number of inodes is limited, as it is
  10 by default, a user cannot soak up an unlimited amount of unreclaimable
  11 dcache memory just by repeatedly linking a file.
  12
  13 But when v3.11 added O_TMPFILE, and the ability to use linkat() on the
  14 fd, we missed accommodating this new case in tmpfs: "df -i" shows that
  15 an extra "inode" remains accounted after the file is unlinked and the fd
  16 closed and the actual inode evicted.  If a user repeatedly links
  17 tmpfiles into a tmpfs, the limit will be hit (ENOSPC) even after they
  18 are deleted.
  19
  20 Just skip the extra reservation from shmem_link() in this case: there's
  21 a sense in which this first link of a tmpfile is then cheaper than a
  22 hard link of another file, but the accounting works out, and there's
  23 still good limiting, so no need to do anything more complicated.
  24
  25 Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1902182134370.7035@eggly.anvils
  26 Fixes: f4e0c30c191 ("allow the temp files created by open() to be linked to")
  27 Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
  28 Signed-off-by: Hugh Dickins <hughd@google.com>
  29 Reported-by: Matej Kupljen <matej.kupljen@gmail.com>
  30 Acked-by: Al Viro <viro@zeniv.linux.org.uk>
  31 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  32 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  33 Signed-off-by: Sasha Levin <sashal@kernel.org>
  34 ---
  35  mm/shmem.c | 10 +++++++---
  36  1 file changed, 7 insertions(+), 3 deletions(-)
  37
  38 diff --git a/mm/shmem.c b/mm/shmem.c
  39 index b6cf0e8e685b..bf13966b009c 100644
  40 --- a/mm/shmem.c
  41 +++ b/mm/shmem.c
  42 @@ -2901,10 +2901,14 @@ static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentr
  43          * No ordinary (disk based) filesystem counts links as inodes;
  44          * but each new link needs a new dentry, pinning lowmem, and
  45          * tmpfs dentries cannot be pruned until they are unlinked.
  46 +        * But if an O_TMPFILE file is linked into the tmpfs, the
  47 +        * first link must skip that, to get the accounting right.
  48          */
  49 -       ret = shmem_reserve_inode(inode->i_sb);
  50 -       if (ret)
  51 -               goto out;
  52 +       if (inode->i_nlink) {
  53 +               ret = shmem_reserve_inode(inode->i_sb);
  54 +               if (ret)
  55 +                       goto out;
  56 +       }
  57
  58         dir->i_size += BOGO_DIRENT_SIZE;
  59         inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
  60 --
  61 2.19.1
  62