| From: "Darrick J. Wong" <darrick.wong@oracle.com> |
| Subject: 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> |
| --- |
| |
| |
| --- a/mm/shmem.c~tmpfs-fix-link-accounting-when-a-tmpfile-is-linked-in |
| +++ a/mm/shmem.c |
| @@ -2854,10 +2854,14 @@ static int shmem_link(struct dentry *old |
| * 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); |
| _ |
