[PATCH] devfs: race fixes and cleanup

From: Andrey Borzenkov <arvidjaar@mail.ru>

- use struct nameidata in devfs_d_revalidate_wait to detect when it is
  called without i_sem hold; take i_sem on parent in this case.  This
  prevents both deadlock with devfs_lookup by allowing it to drop i_sem
  consistently and oops in d_instantiate by ensuring that it always runs
  protected

- remove dead code that deals with major number allocation.  The only
  remaining user was devfs itself and patch changes it to

- use register_chardev to get device number for internal /dev/.devfsd and
  /dev/.statd.

- remove dead auto allocation flag as well

- remove code that does module get on dev open - it is handled by fops_get.
   Use init_special_inode consistently

- get rid of struct cdev_type and bdev_type - both have just single dev_t
  now

fs/devfs/internal.h

-
-extern dev_t devfs_alloc_devnum(umode_t mode);
-extern void devfs_dealloc_devnum(umode_t mode, dev_t devnum);

fs/devfs/util.c

@@ -72,7 +72,6 @@
 #include <linux/vmalloc.h>
 #include <linux/genhd.h>
 #include <asm/bitops.h>
-#include "internal.h"
 
 
 int devfs_register_tape(const char *name)
@@ -96,161 +95,3 @@ void devfs_unregister_tape(int num)
 }
 
 EXPORT_SYMBOL(devfs_unregister_tape);
-
-struct major_list
-{
-    spinlock_t lock;
-    unsigned long bits[256 / BITS_PER_LONG];
-};
-#if BITS_PER_LONG == 32
-#  define INITIALISER64(low,high) (low), (high)
-#else
-#  define INITIALISER64(low,high) ( (unsigned long) (high) << 32 | (low) )
-#endif
-
-/*  Block majors already assigned:
-    0-3, 7-9, 11-63, 65-99, 101-113, 120-127, 199, 201, 240-255
-    Total free: 122
-*/
-static struct major_list block_major_list =
-{SPIN_LOCK_UNLOCKED,
-    {INITIALISER64 (0xfffffb8f, 0xffffffff),  /*  Majors 0-31,    32-63    */
-     INITIALISER64 (0xfffffffe, 0xff03ffef),  /*  Majors 64-95,   96-127   */
-     INITIALISER64 (0x00000000, 0x00000000),  /*  Majors 128-159, 160-191  */
-     INITIALISER64 (0x00000280, 0xffff0000),  /*  Majors 192-223, 224-255  */
-    }
-};
-
-/*  Char majors already assigned:
-    0-7, 9-151, 154-158, 160-211, 216-221, 224-230, 240-255
-    Total free: 19
-*/
-static struct major_list char_major_list =
-{SPIN_LOCK_UNLOCKED,
-    {INITIALISER64 (0xfffffeff, 0xffffffff),  /*  Majors 0-31,    32-63    */
-     INITIALISER64 (0xffffffff, 0xffffffff),  /*  Majors 64-95,   96-127   */
-     INITIALISER64 (0x7cffffff, 0xffffffff),  /*  Majors 128-159, 160-191  */
-     INITIALISER64 (0x3f0fffff, 0xffff007f),  /*  Majors 192-223, 224-255  */
-    }
-};
-
-
-/**
- *	devfs_alloc_major - Allocate a major number.
- *	@mode: The file mode (must be block device or character device).
- *	Returns the allocated major, else -1 if none are available.
- *	This routine is thread safe and does not block.
- */
-
-
-struct minor_list
-{
-    int major;
-    unsigned long bits[256 / BITS_PER_LONG];
-    struct minor_list *next;
-};
-
-static struct device_list {
-	struct minor_list	*first;
-	struct minor_list	*last;
-	int			none_free;
-} block_list, char_list;
-
-static DECLARE_MUTEX(device_list_mutex);
-
-
-/**
- *	devfs_alloc_devnum - Allocate a device number.
- *	@mode: The file mode (must be block device or character device).
- *
- *	Returns the allocated device number, else NODEV if none are available.
- *	This routine is thread safe and may block.
- */
-
-dev_t devfs_alloc_devnum(umode_t mode)
-{
-	struct device_list *list;
-	struct major_list *major_list;
-	struct minor_list *entry;
-	int minor;
-
-	if (S_ISCHR(mode)) {
-		major_list = &char_major_list;
-		list = &char_list;
-	} else {
-		major_list = &block_major_list;
-		list = &block_list;
-	}
-
-	down(&device_list_mutex);
-	if (list->none_free)
-		goto out_unlock;
-
-	for (entry = list->first; entry; entry = entry->next) {
-		minor = find_first_zero_bit (entry->bits, 256);
-		if (minor >= 256)
-			continue;
-		goto out_done;
-	}
-	
-	/*  Need to allocate a new major  */
-	entry = kmalloc (sizeof *entry, GFP_KERNEL);
-	if (!entry)
-		goto out_full;
-	memset(entry, 0, sizeof *entry);
-
-	spin_lock(&major_list->lock);
-	entry->major = find_first_zero_bit(major_list->bits, 256);
-	if (entry->major >= 256) {
-		spin_unlock(&major_list->lock);
-		kfree(entry);
-		goto out_full;
-	}
-	__set_bit(entry->major, major_list->bits);
-	spin_unlock(&major_list->lock);
-
-	if (!list->first)
-		list->first = entry;
-	else
-		list->last->next = entry;
-	list->last = entry;
-
-	minor = 0;
- out_done:
-	__set_bit(minor, entry->bits);
-	up(&device_list_mutex);
-	return MKDEV(entry->major, minor);
- out_full:
-	list->none_free = 1;
- out_unlock:
-	up(&device_list_mutex);
-	return 0;
-}
-
-
-/**
- *	devfs_dealloc_devnum - Dellocate a device number.
- *	@mode: The file mode (must be block device or character device).
- *	@devnum: The device number.
- *
- *	This routine is thread safe and may block.
- */
-
-void devfs_dealloc_devnum(umode_t mode, dev_t devnum)
-{
-	struct device_list *list = S_ISCHR(mode) ? &char_list : &block_list;
-	struct minor_list *entry;
-
-	if (!devnum)
-		return;
-
-	down(&device_list_mutex);
-	for (entry = list->first; entry; entry = entry->next) {
-		if (entry->major == MAJOR(devnum)) {
-			if (__test_and_clear_bit(MINOR(devnum), entry->bits))
-				list->none_free = 0;
-			break;
-		}
-	}
-	up(&device_list_mutex);
-}