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>

3 files changed, 7 insertions, 27 deletions

diff --git a/fs/file_table.c b/fs/file_table.c
index c322794f7360..20002e39754d 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -474,29 +474,6 @@ void file_sb_list_del(struct file *file)
 
 #endif
 
-int fs_may_remount_ro(struct super_block *sb)
-{
-        struct file *file;
-        /* Check that no files are currently opened for writing. */
-        lg_global_lock(files_lglock);
-        do_file_list_for_each_entry(sb, file) {
-                struct inode *inode = file->f_path.dentry->d_inode;
-
-                /* File with pending delete? */
-                if (inode->i_nlink == 0)
-                        goto too_bad;
-
-                /* Writeable file? */
-                if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
-                        goto too_bad;
-        } while_file_list_for_each_entry;
-        lg_global_unlock(files_lglock);
-        return 1; /* Tis' cool bro. */
-too_bad:
-        lg_global_unlock(files_lglock);
-        return 0;
-}
-
 /**
  *      mark_files_ro - mark all files read-only
  *      @sb: superblock in question
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();
diff --git a/fs/super.c b/fs/super.c
index 6acc02237e3e..de41e1e46f09 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -729,10 +729,6 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
                         retval = sb_prepare_remount_readonly(sb);
                         if (retval)
                                 return retval;
-
-                        retval = -EBUSY;
-                        if (!fs_may_remount_ro(sb))
-                                goto cancel_readonly;
                 }
         }