path: root/fs/9p/vfs_inode.c
diff options
authorEryu Guan <eguan@linux.alibaba.com>2018-04-05 16:19:49 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-04-05 21:36:22 -0700
commitac89b2ef9b55924bcf922251f043ba73a32d05bb (patch)
tree7178ec47b68dcf9b4be71228b952cc0e8005789d /fs/9p/vfs_inode.c
parentnet/9p: avoid -ERESTARTSYS leak to userspace (diff)
9p: don't maintain dir i_nlink if the exported fs doesn't either
If the exported filesystem dir on 9p server doesn't maintain accurate i_nlink count, e.g. always reports i_nlink as 1, then 9p should not maintain nlink count either, otherwise drop_link would report warning with i_nlink being zero. For example: - overlayfs sets nlink to 1 for merged dir - ext4 (with dir_nlink feature enabled) sets nlink to 1 if a dir has more than EXT4_LINK_MAX (65000) links. In this case, everytime a stat(2) call (getattr) on such exported dirs on 9p client side, the i_nlink gets reset to 1, then operations like rmdir(2), unlink(2) and rename(2) would cause the dir nlink to go to zero (then negative), which results in warnings in drop_nlink() and/or inc_nlink() calls. This can be reproduced easily as the following steps: - export a merged overlayfs dir via qemu virtfs to guest - mount the exported virtfs in guest - create two sub-directories in the root dir of the mounted 9pfs - stat the root dir of 9pfs, this resets nlink to 1 - remove all subdirs, the second unlink/rmdir would trigger warning ------------[ cut here ]------------ WARNING: CPU: 3 PID: 1284 at fs/inode.c:282 drop_nlink+0x3e/0x50 ... Call Trace: dump_stack+0x63/0x81 __warn+0xcb/0xf0 warn_slowpath_null+0x1d/0x20 drop_nlink+0x3e/0x50 v9fs_remove+0xaa/0x130 [9p] v9fs_vfs_rmdir+0x13/0x20 [9p] vfs_rmdir+0xb7/0x130 do_rmdir+0x1b8/0x230 SyS_unlinkat+0x22/0x30 do_syscall_64+0x67/0x180 ---[ end trace 43758d8ba91e603b ]--- Fix it by leaving i_nlink to be 1 and don't drop nlink if a directory has nlink <= 2, which indicates that the underlying exported fs doesn't maintain nlink count accurately. This follows what ext4 does in ext4_dec_count(). Link: http://lkml.kernel.org/r/20180312053829.4367-1-eguan@linux.alibaba.com Signed-off-by: Eryu Guan <eguan@linux.alibaba.com> Reviewed-by: Yiwen Jiang <jiangyiwen@huawei.com> Tested-by: Roman Kapl <code@rkapl.cz> Cc: Caspar Zhang <caspar@linux.alibaba.com> Cc: Eric Van Hensbergen <ericvh@gmail.com> Cc: Ron Minnich <rminnich@sandia.gov> Cc: Latchesar Ionkov <lucho@ionkov.net> Cc: <v9fs-developer@lists.sourceforge.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/9p/vfs_inode.c')
1 files changed, 22 insertions, 4 deletions
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index bdabb2765d1b..9ee534159cc6 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -579,6 +579,24 @@ static int v9fs_at_to_dotl_flags(int flags)
+ * v9fs_dec_count - helper functon to drop i_nlink.
+ *
+ * If a directory had nlink <= 2 (including . and ..), then we should not drop
+ * the link count, which indicates the underlying exported fs doesn't maintain
+ * nlink accurately. e.g.
+ * - overlayfs sets nlink to 1 for merged dir
+ * - ext4 (with dir_nlink feature enabled) sets nlink to 1 if a dir has more
+ * than EXT4_LINK_MAX (65000) links.
+ *
+ * @inode: inode whose nlink is being dropped
+ */
+static void v9fs_dec_count(struct inode *inode)
+ if (!S_ISDIR(inode->i_mode) || inode->i_nlink > 2)
+ drop_nlink(inode);
* v9fs_remove - helper function to remove files and directories
* @dir: directory inode that is being deleted
* @dentry: dentry that is being deleted
@@ -621,9 +639,9 @@ static int v9fs_remove(struct inode *dir, struct dentry *dentry, int flags)
if (flags & AT_REMOVEDIR) {
- drop_nlink(dir);
+ v9fs_dec_count(dir);
} else
- drop_nlink(inode);
+ v9fs_dec_count(inode);
@@ -1024,12 +1042,12 @@ clunk_newdir:
if (S_ISDIR(new_inode->i_mode))
- drop_nlink(new_inode);
+ v9fs_dec_count(new_inode);
if (S_ISDIR(old_inode->i_mode)) {
if (!new_inode)
- drop_nlink(old_dir);
+ v9fs_dec_count(old_dir);