vfs: prevent remount read-only if pending removes

If there are any inodes on the super block that have been unlinked
(i_nlink == 0) but have not yet been deleted then prevent the
remounting the super block read-only.

Reported-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Tested-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 7 insertions, 0 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 98ebc78b21ab..7e6f2c9dc7c4 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -449,6 +449,10 @@ int sb_prepare_remount_readonly(struct super_block *sb)
         struct mount *mnt;
         int err = 0;
 
+        /* Racy optimization.  Recheck the counter under MNT_WRITE_HOLD */
+        if (atomic_long_read(&sb->s_remove_count))
+                return -EBUSY;
+
         br_write_lock(vfsmount_lock);
         list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
                 if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
@@ -460,6 +464,9 @@ int sb_prepare_remount_readonly(struct super_block *sb)
                         }
                 }
         }
+        if (!err && atomic_long_read(&sb->s_remove_count))
+                err = -EBUSY;
+
         if (!err) {
                 sb->s_readonly_remount = 1;
                 smp_wmb();