ext4: fix #11321: create /proc/ext4/*/stats more carefully

ext4 creates per-suberblock directory in /proc/ext4/ . Name used as
basis is taken from bdevname, which, surprise, can contain slash.

However, proc while allowing to use proc_create("a/b", parent) form of
PDE creation, assumes that parent/a was already created.

bdevname in question is 'cciss/c0d0p9', directory is not created and all
this stuff goes directly into /proc (which is real bug).

Warning comes when _second_ partition is mounted.

http://bugzilla.kernel.org/show_bug.cgi?id=11321

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -2786,14 +2786,20 @@ static int ext4_mb_init_per_dev_proc(struct super_block *sb)
 	mode_t mode = S_IFREG | S_IRUGO | S_IWUSR;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct proc_dir_entry *proc;
-	char devname[64];
+	char devname[BDEVNAME_SIZE], *p;
 
 	if (proc_root_ext4 == NULL) {
 		sbi->s_mb_proc = NULL;
 		return -EINVAL;
 	}
 	bdevname(sb->s_bdev, devname);
+	p = devname;
+	while ((p = strchr(p, '/')))
+		*p = '!';
+
 	sbi->s_mb_proc = proc_mkdir(devname, proc_root_ext4);
+	if (!sbi->s_mb_proc)
+		goto err_create_dir;
 
 	MB_PROC_HANDLER(EXT4_MB_STATS_NAME, stats);
 	MB_PROC_HANDLER(EXT4_MB_MAX_TO_SCAN_NAME, max_to_scan);
@@ -2805,7 +2811,6 @@ static int ext4_mb_init_per_dev_proc(struct super_block *sb)
 	return 0;
 
 err_out:
-	printk(KERN_ERR "EXT4-fs: Unable to create %s\n", devname);
 	remove_proc_entry(EXT4_MB_GROUP_PREALLOC, sbi->s_mb_proc);
 	remove_proc_entry(EXT4_MB_STREAM_REQ, sbi->s_mb_proc);
 	remove_proc_entry(EXT4_MB_ORDER2_REQ, sbi->s_mb_proc);
@@ -2814,19 +2819,24 @@ static int ext4_mb_init_per_dev_proc(struct super_block *sb)
 	remove_proc_entry(EXT4_MB_STATS_NAME, sbi->s_mb_proc);
 	remove_proc_entry(devname, proc_root_ext4);
 	sbi->s_mb_proc = NULL;
+err_create_dir:
+	printk(KERN_ERR "EXT4-fs: Unable to create %s\n", devname);
 
 	return -ENOMEM;
 }
 
 static int ext4_mb_destroy_per_dev_proc(struct super_block *sb)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
-	char devname[64];
+	char devname[BDEVNAME_SIZE], *p;
 
 	if (sbi->s_mb_proc == NULL)
 		return -EINVAL;
 
 	bdevname(sb->s_bdev, devname);
+	p = devname;
+	while ((p = strchr(p, '/')))
+		*p = '!';
 	remove_proc_entry(EXT4_MB_GROUP_PREALLOC, sbi->s_mb_proc);
 	remove_proc_entry(EXT4_MB_STREAM_REQ, sbi->s_mb_proc);
 	remove_proc_entry(EXT4_MB_ORDER2_REQ, sbi->s_mb_proc);