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authorDarrick J. Wong <darrick.wong@oracle.com>2019-02-21 17:48:09 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2019-02-21 18:01:00 +0100
commit1062af920c07f5b54cf5060fde3339da6df0cf6b (patch)
tree42c3494136a9d8338ddfdbeef4db7a726d757b0d /mm/shmem.c
parentpsi: avoid divide-by-zero crash inside virtual machines (diff)
downloadlinux-1062af920c07f5b54cf5060fde3339da6df0cf6b.tar.xz
linux-1062af920c07f5b54cf5060fde3339da6df0cf6b.zip
tmpfs: fix link accounting when a tmpfile is linked in
tmpfs has a peculiarity of accounting hard links as if they were separate inodes: so that when the number of inodes is limited, as it is by default, a user cannot soak up an unlimited amount of unreclaimable dcache memory just by repeatedly linking a file. But when v3.11 added O_TMPFILE, and the ability to use linkat() on the fd, we missed accommodating this new case in tmpfs: "df -i" shows that an extra "inode" remains accounted after the file is unlinked and the fd closed and the actual inode evicted. If a user repeatedly links tmpfiles into a tmpfs, the limit will be hit (ENOSPC) even after they are deleted. Just skip the extra reservation from shmem_link() in this case: there's a sense in which this first link of a tmpfile is then cheaper than a hard link of another file, but the accounting works out, and there's still good limiting, so no need to do anything more complicated. Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1902182134370.7035@eggly.anvils Fixes: f4e0c30c191 ("allow the temp files created by open() to be linked to") Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Hugh Dickins <hughd@google.com> Reported-by: Matej Kupljen <matej.kupljen@gmail.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/shmem.c')
-rw-r--r--mm/shmem.c10
1 files changed, 7 insertions, 3 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 6ece1e2fe76e..0905215fb016 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2854,10 +2854,14 @@ static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentr
* No ordinary (disk based) filesystem counts links as inodes;
* but each new link needs a new dentry, pinning lowmem, and
* tmpfs dentries cannot be pruned until they are unlinked.
+ * But if an O_TMPFILE file is linked into the tmpfs, the
+ * first link must skip that, to get the accounting right.
*/
- ret = shmem_reserve_inode(inode->i_sb);
- if (ret)
- goto out;
+ if (inode->i_nlink) {
+ ret = shmem_reserve_inode(inode->i_sb);
+ if (ret)
+ goto out;
+ }
dir->i_size += BOGO_DIRENT_SIZE;
inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);